Case Studies
 
This section contains Case Studies covering all ASE Areas.
Quick Links - Click on an ASE photo below to jump to it's content
           
  (A0) Basic Skills   (A1) Engine Repair   (A2) Automatic Transmission   (A3) Manual Drive Train Axles   (A4) Suspension and Steering  
                     
           
  (A5) Brakes   (A6) Electrical / Electronic Systems   (A7) Heating and Air Conditioning   (A8) Engine Performance   (A9) Light Diesel  
                     
 
The Case of the Rusty Air Impact Wrenches
In one busy shop, it was noticed by several technicians that water was being pumped through the air compressor lines and out of the vents of air impact wrenches whenever they were used. It is normal for moisture in the air to condense in the air storage tank of an air compressor. One of the routine service procedures is to drain the water from the air compressor. The water had been drained regularly from the air compressor at the rear of the shop, but the problem continued. Then someone remembered that there was a second air compressor mounted over the parts department. No one could remember ever draining the tank from that compressor. After that tank was drained, the problem of water in the lines was solved.
 
SUMMARY:  
Complaint Water was found in the air lines in the shop.
Cause Water was found in the second compressor above the parts department.
Correction The service manager assigned a person to drain water from both compressors everyday. The water problem was solved.
 
Owner's Manual is the Key to Proper Operation
A customer purchased a used Pontiac Vibe and complained to a shop that the cruise control would disengage and had to be reset if driven below 25 mph (40 km/h). The service technician was able to verify that in fact this occurred, but did not know if this feature was normal or not. The technician checked the owner’s manual and discovered that this vehicle was designed to operate this way. Unlike other cruise control systems, those systems on Toyota-based vehicles are designed to shut off below 25 mph, requiring the driver to reset the desired speed. The customer was informed that nothing could be done to correct this concern and the technician also learned something.
 
SUMMARY:  
Complaint The owner of a Ponitiac Vibe complained that the cruise control would stop working if the speed dropped below 25 mph.
Cause The owner’s manual indicated that this is normal operation.
Correction The customer was informed that this is normal operation and that no repair is needed or required.
 

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A Technician's Toughie
The owner of a Honda Civic complained that engine did not run smoothly and the “Check Engine“ light was on. The service technician retrieved a P0300 (random misfire detected) as well as a P0303 ( cylinder number three misfire detected). A scope was connected to each of the coils one at a time and the secondary pattern looked perfect on all four cylinders. All four coils and spark plugs were removed yet they all looked normal. The spark plug for cylinder #3 was moved to cylinder #1 and then the coils were re-installed and the vehicle driven on a test drive. A P0301 was then retrieved which indicated that the problem was due to the spark plug itself. Replacing the spark plug with a new one solved the misfire problem. The plug was apparently cracked yet not seen. The scope showed a normal secondary pattern because the voltage needed to jump to ground through the crack in the plug was about the same as would be required to jump the gap inside the combustion chamber.
 
SUMMARY:  
Complaint Customer stated that the engine ran poorly.
Cause Tests confirmed that one spark plug was found to be cracked.
Correction Replacing the spark plug solved the engine misfire problem.
 
Big Problem, No Noise
Sometimes the piston pin can “walk” off the center of the piston and score the cylinder wall. This scoring is often not noticed because this type of wear does not create noise. Because the piston pin is below the piston rings, little combustion pressure is lost past the rings until the groove worn by the piston pin has worn the piston rings. Troubleshooting the exact cause of the increased oil consumption is difficult because the damage done to the oil control rings by the groove usually affects only one cylinder. Often, compression tests indicate good compression because of the cylinder seals, especially at the top. More than one technician has been surprised to see the cylinder gouged by a piston pin when the cylinder head has been removed for service. In such a case, the cost of the engine repair immediately increases far beyond that of normal cylinder head service.
 
SUMMARY:  
Complaint Engine was burning oil yet the compression was good leading the technician to remove the head.
Cause A piston pin had moved and scored the cylinder wall.
Correction The engine was replaced to correct the oil burning concern.
 
Engine Noise
An experienced technician was assigned to diagnose a loud engine noise. The noise sounded like a defective connecting rod bearing or other major engine problem. The alternator belt was found to be loose. Knowing that a loose belt can “whip” and cause noise, the belt was inspected and the alternator moved on its adjustment slide to tighten the belt. After tightening the belt, the engine was started and the noise was still heard. After stopping the engine, the technician found that the alternator belt was still loose. The problem was discovered to be a missing bolt that attached the alternator mounting bracket to the engine. The forces on the alternator caused the bracket to hit the engine. This noise was transmitted throughout the engine. Replacing the missing bracket bolt solved the loud engine noise and pleased a very relieved owner.
 
SUMMARY:
Complaint Customer complained of a loud engine noise.
Cause Missing alternator bracket bolt.
Correction Installed missing alternator bracket bolt.
If 50% Is Good, 100% Must Be Better
A vehicle owner said that the cooling system of his vehicle would never freeze or rust. He said that he used 100% antifreeze (ethylene glycol) instead of a 50/50 mixture with water. However, after the temperature dropped to −20°F (−29°C), the radiator froze and cracked. (Pure antifreeze freezes at about 0°F [−18°C].) After thawing, the radiator had to be replaced. The owner was lucky that the engine block did not also crack. For best freeze protection with good heat transfer, use a 50/50 mixture of antifreeze and water. As the percentage of antifreeze increases, the boiling temperature increases, and freezing protection increases (up to 70% antifreeze), but the heat transfer performance of the mixture decreases.
 
SUMMARY:  
Complaint The coolant froze and cracked the radiator.
Cause Vehicle owner used 100% antifreeze instead of the recommended 50/50 mixture of antifreeze and water.
Correction The radiator was replaced and the proper mixture of antifreeze/water was used as the coolant.
 
Highway Overheating
A vehicle owner complained of an overheating vehicle, but the problem occurred only while driving at highway speeds. The vehicle, equipped with a 4-cylinder engine, would run in a perfectly normal manner in city driving situations. The technician flushed the cooling system and replaced the radiator cap and the water pump, thinking that restricted coolant flow was the cause of the problem. Further testing revealed coolant spray out of one cylinder when the engine was turned over by the starter with the spark plugs removed. A new head gasket solved the problem. Obviously, the head gasket leak was not great enough to cause any problems until the engine speed and load created enough flow and heat to cause the coolant temperature to soar. The technician also replaced the oxygen (O2)sensor.
 
SUMMARY:  
Complaint Customer stated that the engine would overheat but only if driven at highway speed.
Cause The root cause was determined to be a defective head gasket.
Correction The head gasket was replaced and the oxygen sensor was also replaced because coolant can cause the sensor to read incorrectly. Replacing the oxygen sensor was done to be insured that the engine ran correctly.
 
"Oops"
After overhauling a big block Ford V-8 engine, the technician used an electric drill to rotate the oil pump with a pressure gauge connected to the oil pressure sending unit hole. When the electric drill was turned on, oil pressure would start to increase (to about 10 PSI), then drop to zero. In addition, the oil was very aerated (full of air). Replacing the oil pump did not solve the problem. After hours of troubleshooting and disassembly, it was discovered that an oil gallery plug had been left out underneath the intake manifold. The oil pump was working correctly and pumped oil throughout the engine and out of the end of the unplugged oil gallery. It did not take long for the oil pan to empty and the oil pump began drawing in air that aerated the oil which caused the oil pressure to drop. Installing the gallery plug solved the problem.
Note: Many overhead camshaft engines use an oil passage check valve in the block near the deck. The purpose of this valve is to hold oil in the cylinder head around the camshaft and lifters when the engine is stopped. Failure to reinstall this check valve can cause the valve train to be noisy after engine start-up.
 
SUMMARY:  
Complaint Newly overhauled engine lost oil pressure shortly after start up.
Cause An oil gallery plug was found to be missing.
Correction The missing plug was installed and after reassembly, the engine oil pressure was normal.
 
S-10 Pickup Truck Frame Noise
The owner of a Chevrolet S-10 pickup truck complained of a loud squeaking noise, especially when turning left. Several technicians attempted to solve the problem and replaced shock absorbers, ball joints, and control arm bushings without solving the problem. The problem was finally discovered to be the starter motor hitting the frame. A measurement of new vehicles indicated that the clearance between the starter motor and the frame was about 1/8 inch (0.125 inch) (0.3 cm)! The sagging of the engine mount and the weight transfer of the engine during cornering caused the starter motor to rub up against the frame. The noise was transmitted through the frame throughout the vehicle and made the source of the noise difficult to find.
 
SUMMARY:
Complaint Owner complained of a loud squeaking noise.
Cause The starter was found to be hitting the frame due to a collapsed engine mount.
Correction Both engine mounts were replaced, which proved to be the root cause.
 
The Blazer Story
The owner of a Chevrolet Blazer equipped with a 4.3 liter V-6 engine complained that the engine would stumble and hesitate at times. Everything seemed to be functioning correctly, except that the service technician discovered a weak vacuum going to the EGR valve at idle. This vehicle was equipped with an EGR valve-control solenoid, called an electronic vacuum regulator valve (EVRV) by General Motors Corporation. The computer pulses the solenoid to control the vacuum that regulates the operation of the EGR valve. The technician checked the service manual for details on how the system worked. The technician discovered that vacuum should be present at the EGR valve only when the gear selector indicates a drive gear (drive, low, reverse). Because the technician discovered the vacuum at the solenoid to be leaking, the solenoid was obviously defective and required replacement. After replacement of the solenoid (EVRV), the hesitation problem was solved.
 
SUMMARY:  
Complaint Vehicle owner complained that the engine would stumble and hesitate at times.
Cause The EGR vacuum solenoid was found to be leaking.
Correction The EGR solenoid was replaced which restored proper engine operation.
 
The Case of the No Crank
A 4-cylinder engine would not crank. Previously the customer said that once in a while, the starter seemed to lock up when the vehicle sat overnight but would then finally crank. The vehicle finally would not start and was towed to the shop. The service technician checked the current draw of the starter and it read higher than the scale on the ammeter. The technician then attempted to rotate the engine by hand and found that the engine would not rotate. Based on this history of not cranking normally in the morning, the technician removed the spark plugs and attempted to crank the engine. This time the engine cranked and coolant was seen shooting from cylinders 2 and 3. Replacing the bad gasket solved the cranking problems in the morning.
 
SUMMARY:  
Complaint Engine would not crank after sitting overnight.
Cause Blown head gasket caused coolant to enter the cylinder prevent the engine from rotating.
Correction Replacing the head gasket solved the no cranking issue.
 
The Case of the Retarted Exhaust Camshaft
A Toyota equipped with a double overhead camshaft (DOHC) inline six-cylinder engine failed the statemandated enhanced exhaust emissions test for NOx. The engine ran perfectly without spark knocking (ping), which is usually a major reason for excessive NOx emissions. The technician checked the following:
• The ignition timing, which was found to be set to specifications (if too far advanced, can cause excessive NOx)
• The cylinders, which were decarbonized using top engine cleaner
• The EGR valve, which was inspected and the EGR passages cleaned
After all the items were completed, the vehicle was returned to the inspection station where the vehicle again failed for excessive NOx emissions ( better, but still over the maximum allowable limit). After additional hours of troubleshooting, the technician decided to go back to basics and start over again. A check of the vehicle history with the owner indicated that the only previous work performed on the engine was a replacement timing belt over a year before. The technician discovered that the exhaust cam timing was retarted two teeth, resulting in late closing of the exhaust valve. The proper exhaust valve timing resulted in a slight amount of exhaust being retained in the cylinder. This extra exhaust was added to the amount supplied by the EGR valve and helped reduce NOx emissions. After repositioning the timing belt, the vehicle passed the emissions test well within the limits.
 
SUMMARY:
Complaint Customer stated that the vehicle failed an emission test due to excessive NOx exhaust emissions.
Cause The exhaust cam was discovered to be retarted by two teeth as a result of the timing belt being incorrectly installed during a previous repair.
Correction The timing belt was properly aligned and the vehicle passed the emission test.
 
The Case of the Wrong Oil
A 2007 Dodge Durango was in the shop for routine service, including a tire rotation and an oil change. Shortly after, the customer returned and stated that the “check engine” light was on. A scan tool was used to retrieve any diagnostic trouble codes. A P0521, “oil pressure not reaching specified value at 1250 RPM” was set. A check of service information showed that this code could be set if the incorrect viscosity engine oil was used. The shop had used SAE 10W-30 but the 5.7 liter Hemi V-8 with multiple displacement system (MDS) required SAE 5W-20 oil. The correct oil was installed and the DTC cleared. A thorough test-drive confirmed that the fault had been corrected and the shop learned that the proper viscosity oil is important to use in all vehicles.
 
SUMMARY:  
Complaint The check engine light was on after an oil change.
Cause The incorrect viscosity oil was used.
Correction The oil was replaced with the specified viscosity and the DTC was cleared.
 
The Case of the Wrong Oil Viscosity
A Dodge Durango 5.7 liter Hemi with a multiple displacement system (MDS) had the oil changed at a shop. SAE 10W-30 was used as this was the “standard” bulk oil in the shop. After the oil change, the vehicle was returned to the customer. Within a few minutes, however, the “check engine” light came on. The technician checked for diagnostic trouble codes (DTCs) and found a P0521 DTC stored. The technician checked service information and discovered that the code could be set if the incorrect viscosity engine oil had been used. The description of the P0521 read: “Oil pressure not reaching specified at 1250 RPM.” The technician changed the oil and used the specified SAE 5W-20, then cleared the DTC. A test drive confirmed that the change to the correct viscosity oil solved the problem.
 
SUMMARY:  
Complaint Customer stated that the “check engine” came on after an oil change.
Cause The incorrect viscosity of oil was used.
Correction The specified viscosity oil (SAE 5W-20) was used and the code cleared.
 
The Cavalier Convertible Story
The owner of a Cavalier convertible stated to a service technician that the “check engine” (MIL) was on. The technician found a diagnostic trouble code (DTC) for a MAP sensor. The technician removed the hose at the MAP sensor and discovered that gasoline had accumulated in the sensor and dripped out of the hose as it was being removed. The technician replaced the MAP sensor and test drove the vehicle to confirm the repair. Almost at once the check engine light came on with the same MAP sensor code. After several hours of troubleshooting without success in determining the cause, the technician decided to start over again. Almost at once, the technician discovered that no vacuum was getting to the MAP sensor where a vacuum gauge was connected with a T-fitting in the vacuum line to the MAP sensor. The vacuum port in the base of the throttle body was clogged with carbon. After a thorough cleaning, and clearing the DTC, the Cavalier again performed properly and the check engine light did not come on again. The technician had assumed that if gasoline was able to reach the sensor through the vacuum hose, surely vacuum could reach the sensor. The technician learned to stop assuming when diagnosing a vehicle and concentrate more on testing the simple things first.
 
SUMMARY:  
Complaint Customer stated that the “Check Engine” warning light was on.
Cause The vacuum post to the MAP sensor was found to be clogged.
Correction Cleaning the vacuum port at the throttle body restored proper operation of the MAP sensor.
 
The Collapsed Radiator Hose Story
An automotive student asked the automotive instructor what brand of radiator hose is the best. Not knowing exactly what to say, the instructor asked if there was a problem with the brand hose used. The student had tried three brands and all of them collapsed when the engine cooled. The instructor then explained that the vehicle needed a new pressure cap and not a new upper radiator hose. The student thought that because the lower hose did not collapse that the problem had to be a fault with the hose. The instructor then explained that the lower radiator hose has a spring inside to keep the lower hose from collapsing due to the lower pressure created at the inlet to the water pump. The radiator cap was replaced and the upper radiator hose did not collapse when the engine cooled.
 
SUMMARY:  
Complaint Vehicle owner stated the upper radiator hose would collapse when the engine cools.
Cause The upper radiator collapsed due to a fault with the radiator pressure cap.
Correction A new radiator cap solved the problem.
 
The Dirty MAF Sensor Story
The owner of a Buick Park Avenue equipped with a 3,800 V-6 engine complained that the engine would hesitate during acceleration, showed lack of power, and seemed to surge or miss at times. A visual inspection found everything to be like new, including a new air filter. There were no stored diagnostic trouble codes (DTCs). A look at the scan data showed airflow to be within the recommended 3 to 7 grams per second. A check of the frequency output showed the problem.
Idle frequency ∙ 2.177 kHz (2,177 Hz). Normal frequency at idle speed should be 2.37 to 2.52 kHz. Cleaning the hot wire of the MAF sensor restored proper operation. The sensor wire was covered with what looked like fine fibers, possibly from the replacement air filter.
 
SUMMARY:  
Complaint Customer stated that the engine hesitated when accelerating.
Cause Tests confirmed that the MAF sensor was was operating correctly but the frequency output at idle was not within the normal range.
Correction Cleaning the MAF sensor restored proper operation of the sensor and the engine now accelerates normally.
 
The Low Oil Pressure Story
After replacing valve cover gaskets on a Chevrolet V-8, the technician discovered that the oil pressure warning lamp was on. After checking the oil level and finding everything else okay, the technician discovered a wire pinched under the valve cover. The wire went to the oil pressure sending unit. The edge of the valve cover had cut through the insulation and caused the current from the oil lamp to go to ground through the engine. Normally the oil lamp comes on when the sending unit grounds the wire from the lamp. The technician freed the pinched wire and covered the cut with silicone sealant to prevent corrosion damage.
 
SUMMARY:
Complaint The technician noticed that the oil pressure warning light was on after replacing a valve cover gasket.
Cause A visual inspection discovered a pinched wire to the oil pressure switch was the cause.
Correction The pinched wire was freed and sealed restoring the proper operation of the oil pressure warning light circuit.
 
The Mysterious Engine Vibration
A Buick 3.8 liter V-6 engine vibrated the whole car after a new short block had been installed. The technician who had installed the replacement engine did all of the following:
1. Checked the spark plugs
2. Checked the spark plug wires
3. Disconnected the torque converter from the flex plate (drive plate) to eliminate the possibility of a torque converter or automatic transmission pump problem
4. Removed all accessory drive belts one at a time Yet the vibration still existed. Another technician checked the engine mounts and found that the left (driver’s side) engine mount was out of location, ripped, and cocked. The transmission mount was also defective. After the technician replaced both mounts and made certain that all mounts were properly set, the vibration was eliminated.
 
SUMMARY:
Complaint Vehicle vibrated after a replacement engine block was installed.
Cause Defective engine and transmission mounts.
Correction Both mounts were replaced which corrected the vibration.
 
The Noisy Camshaft
The owner of an overhead cam 4-cylinder engine complained of a noisy engine. After taking the vehicle to several technicians and getting high estimates to replace the camshaft and followers, the owner tried to find a less expensive solution. Finally, another technician replaced the serpentine drive belt on the front of the engine and “cured” the “camshaft” noise for a fraction of the previous estimates.
Many engines have been disassembled and/or overhauled because of a noise that was later determined to be from one of the following:
• Loose or defective accessory drive belt(s)
• Loose torque converter-to-flex plate (drive plate) bolts (nuts)
• Defective mechanical fuel pump (if equipped)
 
SUMMARY:  
Complaint Vehicle owner complained about an noisy engine.
Cause A defective accessory drive belt was found to be the cause of the noise.
Correction The accessory drive belt was replaced.
 
The Oil Burning Chevrolet Astro Van
An automotive instructor was driving a Chevrolet Astro van to Fairbanks, Alaska, in January. It was pretty cold out, somewhere around -32°F (-36°C). As he pulled into Fairbanks and stopped at a traffic light, he smelled burning oil. When he stopped at the hotel he still smelled burning oil. He looked under the van and discovered a large pool of oil. After checking the oil and finding very little left, he called a local shop and was told to bring it in. The technician looked over the situation and said, “You need to put some cardboard across the grill to stop the PCV valve from freezing up.” Apparently the PCV valve froze, which then caused the normal blowby gases to force several quarts out the dipstick tube. After he installed the cardboard, he did not have any further problems.
Caution: Do not cover the radiator when driving unless under severe cold conditions and carefully watch the coolant temperature to avoid overheating the engine.
SUMMARY:  
Complaint Vehicle owner experienced oil burning when extremely cold outside.
Cause The PCV valve was frozen causing pressure to build up in the crankcase.
Correction Placing some cardboard in front of the radiator prevented the valve from freezing and allowed the crankcase ventilations system to function normally.
 
The Start/Stall/Start/Stall Problem
A Chevrolet 4-cylinder engine would stall every time it was started. The engine cranked normally and the engine started quickly. It would just stall once it had run for about 1 second. After hours of troubleshooting, it was discovered that if the “gages” fuse was removed, the engine would start and run normally. Because the alternator was powered by the “gages” fuse, the charging voltage was checked and found to be over 16 volts just before the engine stalled. Replacing the alternator fixed the problem. The computer shut down to prevent damage when the voltage exceeded 16 volts.
 
SUMMARY:  
Complaint Engine would stall every time it started.
Cause The alternator was over charging causing the PCM to shut off the engine to protect itself against the higherthan- normal voltage.
Correction Replacing the alternator corrected the engine stall after start concern.
 
The Two Minute Alternator Repair
A Chevrolet pickup truck was brought to a dealer for routine service. The owner stated that the battery required a jump start after a weekend of sitting. The technician tested the battery and charging system voltage using a small handheld digital multimeter. The battery voltage was 12.4 volts (about 75% charged), but the charging voltage was also 12.4 volts at 2000 RPM. Because normal charging voltage should be 13.5 to 15 volts, it was obvious that the charging system was not operating correctly. The technician checked the dash and found that the “charge” light was not on. Before removing the alternator for service, the technician checked the wiring connection on the alternator. When the lead regulator connector was removed, the connector was discovered to be rusty. After the contacts were cleaned, the charging system was restored to normal operation. The technician had learned that the simple things should always be checked first before tearing into a big (or expensive) repair.
 
SUMMARY:  
Complaint Battery was dead after sitting over the weekend.
Cause The alternator was not charging due to a poor electrical connection at the alternator.
Correction The electrical connector was cleaned and the charging system was restored to normal operation.
 
The Weird Running Chevrolet Truck
An older Chevrolet pickup truck equipped with a V-8 engine was towed into a shop because it would not start. A quick check of the ignition system showed that the pickup coil had a broken wire below it and the ignition control module. The distributor was removed from the engine and the distributor shaft was removed, cleaned, and a replacement pickup coil was installed. The engine started but ran rough and hesitated when the accelerator pedal was depressed. After an hour of troubleshooting, a careful inspection of the new pickup coil showed that the time core had six instead of eight points, meaning that the new pickup coil was meant for a V-6 instead of a V-8 engine. Replacing the pickup coil again solved the problem.
 
SUMMARY:  
Complaint Customer stated that the truck would not start.
Cause A visual inspection was used to determine a that a pickup coil wire was broken and was replaced but with the wrong part that was in the correct box.
Correction Replacing the pickup coil with the right part fixed the truck.
 
The Whistling Engine
An older vehicle was being diagnosed for a whistling sound whenever the engine was running, especially at idle. It was finally discovered that the breather in the valve cover was plugged and caused high vacuum in the crankcase. The engine was sucking air from what was likely the rear main seal lip, making the “whistle” noise. After replacing the breather and PCV, the noise stopped.
 
SUMMARY:  
Complaint Vehicle owner complained that the engine would make a whistling noise.
Cause The crankcase breather was clogged.
Correction The breather and the PCV valve were both replaced which stopped the whistling noise when the engine was running.
 
Valve Springs Can Vary
A technician was building a small block Chevrolet V-8 and found that many of the valve springs did not have the same tension. Using a valve spring tester, the technician visited a local parts store and measured all of the valve springs that the store had in stock. The technician selected and purchased the 16 valve springs that were within specification and within a very narrow range of tension. Although having all valve springs equal may or may not affect engine operation, the technician was pleased that all of the valve springs were equal.
 
SUMMARY:  
Complaint A technician discovered that valve springs did not all have the same tension.
Cause Due to manufacturing tolerances, valve springs can vary in tension.
Correction The technician tested all available springs and selected those that were the most equal in tension.
 

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Look for Previous Repairs
A technician was asked to fix the speedometer on a Pontiac Grand Am that showed approximately double the actual speed. Previous repairs had included a new vehicle speed (VS) sensor and computer. Nothing made any difference. The customer stated that the problem happened all of a sudden. After hours of troubleshooting, the customer just happened to mention that the automatic transaxle had been repaired shortly before the speedometer problem. The root cause of the problem was discovered when the technician learned that a final drive assembly from a 4T60-E transaxle had been installed on the 3T-40 transaxle. The 4T60-E final drive assembly has 13 reluctor teeth, whereas the 3T-40 has 7 teeth. This difference in the number of teeth caused the speedometer to read almost double the actual vehicle speed. After the correct part was installed, the speedometer worked correctly. The technician now always asks if there has been any recent work performed in the vehicle prior to any diagnosis.
 
SUMMARY:
Complaint Customer stated that the speedometer was reading about double the actual speed.
Cause The incorrect final drive had been installed during a transaxle repair which had the wrong number of reluctor teeth.
Correction Replacing the final drive with the proper part fixed the speedometer error concern.
 

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Find the Root Cause
The transmission in a Ford Explorer (150,000 mi) was rebuilt 5,000 miles ago. A damaged input shaft and all of the bearings were replaced using original equipment parts. The end play was adjusted as shown in the Ford service information. This transmission was repaired before for the same problem, a seized front bearing. It came back because of the same problem. It was determined that the damage was caused by a fluid loss. The leak was through three loose rubber plugs at the back of the top cover. Replacement of the damaged input shaft bearing and the three rubber sealing plugs fixed this problem.
 
SUMMARY:
Complaint Repeated bearing failure.
Cause Leaking seals.
Correction Replacement bearings and new seals corrected the root cause.
 
I Used to Have a Limited Slip Differential
An owner of a Chevrolet S-10 pickup truck equipped with a V-6 and five-speed manual transmission complained that he used to be able to spin both rear tires on dry pavement, but lately only one tire spins. Many General Motors pickup trucks are equipped with an Eaton locking differential that uses a torque limiting disc. The teeth of this disc are designed to shear to prevent the possibility of breaking an axle. The service procedure to correct the customer’s concern is to replace the left-hand clutch plates. Usually, the shearing of the torque-linking teeth is associated with a loud bang in the rear axle. The differential will continue to operate normally as a standard (open) differential.
 
SUMMARY:
Complaint Driver complained that only one rear wheel would spin when accelerating.
Cause A torque-limiting disc was sheared.
Correction The left side clutch plates were replaced and the proper operation of the drive axle was restored to normal operation.
 
Pinion Bearing Fault
An all-wheel-drive (AWD) Buick Rendezvous (61,000 mi) came into the shop with a loud drivetrain howl and vibration that varied with speed and load. Raising the vehicle on a hoist allowed the technician to narrow the problem down to the rear drive axle. The rear drive axle gear oil was clean and at the proper level. A close inspection of the drive axle revealed rough pinion shaft bearings. The technician was unable to get replacement bearings or a rebuilt assembly so a new axle was installed, which fixed the problem.
 
SUMMARY:
Complaint Customer complained of a loud howl sound and vibration that varied with speed and load.
Cause Rough pinion bearings.
Correction A replacement drive axle solved the noise and vibration concern.
 
The Case of the Broken Chevrolet Clutch
The clutch in a Chevrolet HHR (119,000 mi) would not disengage. A broken pressure plate or clutch disc was suspected, so the transaxle was removed. Inspection showed normal clutch wear, nothing to prevent disengagement. A new pressure plate, disc, and throwout bearing were installed, and the flywheel was machined. The clutch still would not disengage. A small leak was found at the slave cylinder, so the entire hydraulic system was replaced with a new assembly. The new assembly was full of fluid, so bleeding was not necessary. The slave cylinder push rod travel has normal movement during clutch pedal travel application. At the suggestion of the parts supplier, a flywheel shim was installed to compensate for the thinner machined flywheel, but this did not help. Close inspection revealed that the release fork was bent and worn. Replacement of the fork and its bushings fixed this problem.
 
SUMMARY:
Complaint Clutch would not disengage.
Cause The release fork was worn and bent.
Correction Replacing the fork and the bushings corrected this customer concern.
 
The Case of the Broken Chevrolet Suburban
The transfer case of a Chevrolet Suburban would jump into neutral when the vehicle hit a large dip or bump in the road. The vehicle could be shifted back into gear and driven. After disassembly of the transfer case, it was found that the plastic shift fork inserts had broken off. Replacement of the shift forks fixed this problem.
 
SUMMARY:
Complaint Customer was concerned that the transfer case would go into neutral when driving over rough or uneven pavement.
Cause The plastic shift fork inserts had broken off.
Correction Replaced the transfer case shift forks.
 
The Case of the Broken Jeep
A Jeep Wrangler (73,500 mi) front axle would not engage. An inspection showed broken and brittle vacuum hoses, some falling off their connectors. The vacuum harness to the vacuum hubs was replaced, which did not fix the problem. However, after looking at a vacuum diagram, it was determined that a clogged vent could be the cause. A visual inspection revealed that the vent was plugged with mud. Cleaning this vent fixed this problem.
 
SUMMARY:
Complaint Customer was concerned about the front axle not being able to engage.
Cause Vent port was clogged.
Correction Replaced the vacuum hoses and lines and cleaned the vent.
 
The Case of the Broken Kia
A Kia SUV (63,000 mi) came in with an inoperative 4WD. This vehicle uses vacuum-operated front hubs. Rotted flexible front hub vacuum lines and plugged steel vacuum lines were replaced, but this did not help. New hubs had previously been installed. The technician found that a seal failure had apparently allowed vacuum to suck all of the grease out of the wheel bearing. This grease probably caused the plugged and rotted vacuum lines, and the grease loss caused wheel and spindle bearing failure. Replacement of the wheel bearings, spindle bearing, spindle, and seal with updated parts fixed this problem.
 
SUMMARY:
Complaint Customer was concerned about a lack of 4WD.
Cause Front vacuum hub seals were at fault.
Correction Replaced wheel bearings, spindle and seal with updated parts.
 
The Case of the Hard Shifting Honda
A Honda Civic (140,000 mi) came in with a hard shifting concern. A road test confirmed that the car shifted hard into every gear. There was no grinding that would indicate a clutch problem. The fluid level was good, and seemed to be SAE 5W-30 engine oil. The technician drained, flushed, and filled the transaxle with Honda manual transmission fluid (MTF), and this fixed the hard shift problem.
 
SUMMARY:
Complaint Owner complained of hard shifting.
Cause Appeared to have had engine oil instead of Honda manual transmission fluid.
Correction Replaced the transaxle fluid with the specified fluid.
 
The Case of the Missing Bleeder
The clutch failed in the Nissan 300ZX (181,000 mi) because the clutch arm pivot ball broke, which allowed the slave cylinder to come apart. The broken part along with the slave cylinder, clutch disc, pressure plate, and release bearing were replaced. But, the clutch pedal would go to the floor without releasing the clutch. The clutch master cylinder was replaced, and a clutch adjustment was made. The clutch worked so the vehicle was returned to the customer, but a few days later it returned with a slipping clutch. The technician discovered that a bleeder screw was located near the right headlight. Opening this bleeder let a lot of air out of the clutch line. Completely bleeding the clutch along with a free travel readjustment fixed this comeback.
 
SUMMARY:
Complaint Customer complained about a slipping clutch shortly after the clutch was replaced.
Cause Air was found in the hydraulic clutch line.
Correction The clutch system bleeder valve was located behind the right headlight and the system bled which corrected the slipping clutch concern.
 
The Case of the Noisy Chevrolet Pickup Truck
A GMC pickup (42,000 mi) had a noise in 4WD and would not shift out of 4WD until coasting in second gear. A test using an electronic noise detecting device such as Chassis Ears®, indicated the whining noise was coming from the transfer case. A careful check of tire size showed 5/32 inch deeper tread on the rear tires, and a check of tire circumference showed 98 inches at the front and 99 inches at the rear. Replacement of the worn front tires fixed this problem. Apparently, the mix-matched tire sizes caused the drivetrain to bind, which prevented the transfer case to lock up and not be able to be shifted correctly.
 
SUMMARY:
Complaint Customer was concerned about a noise and not being able to shift out of 4WD.
Cause Front tires were worn and smaller than the rear tires.
Correction Replaced both front tires.
 
The Case of the Noisy Range Rover
A Land Rover, Range Rover (100,000 mi) has a ratcheting type noise that seems to be coming from the back seat. The transfer case was removed and disassembled. The chain appeared to be stretched because the new, replacement chain was about an inch shorter. Replacement of the drive chain fixed this problem.
 
SUMMARY:
Complaint Customer was concerned about a noise coming from the back seat.
Cause Stretched transfer case chain.
Correction Replaced transfer case chain.
 
The Case of the Skipping Chevrolet Minivan
An AWD Chevrolet SUV (38,000 mi) had an odd skipmiss feeling during acceleration. Tire circumferences were checked, and they were within 1/8” of each other. The transfer case was drained and refilled with the proper fluid, but this did not help. A second transfer case fluid change was recommended, and this fixed the problem. This transfer case can have a stick/slip problem, similar to a limited slip differential. Apparently, the second fluid change caused the clutch plates to work normally.
 
SUMMARY:
Complaint Customer was concerned about a skip-miss feeling during acceleration.
Cause The fluid in the transfer case was causing the the sticking/slip issue.
Correction The transfer case fluid was replaced two times which corrected the customer concern.
 
The Case of the Stepped-Type Flywheel
The clutch in a 2005 VW (107,000 mi) has been replaced and the flywheel was resurfaced at the same time. But now there is noticeable clutch chatter. The technician was told that during the flywheel resurfacing, only the clutch mating surface was machined. The technician feels that the step height could be incorrect, but could not find the specification. After contacting international Automotive Technician Network (iATN), a fellow technician provided the step-height specification. A check of the flywheel showed that its step was at the limit, but the clutch surface also had 0.003 inch of runout. Machining the flywheel fixed this problem.
 
SUMMARY:
Complaint The technician discovered a clutch chatter after the clutch had been replaced.
Cause Measuring the flywheel showed excessive runout.
Correction The flywheel was machined which corrected the clutch chatter concern.
 
The Case of the Stuck in Gear Jeep
A Jeep Wrangler (120,000 mi) sometimes got stuck in first or reverse, and the only way to get it out of gear is to shut the engine off. The transmission shifted okay most of the time. Thinking that clutch or related components were the most likely cause, the transmission was removed, and an inspection revealed a seizing pilot bushing. Replacement of the bushing fixed this problem. The pilot bushing did not allow the input shaft to move independently of the flywheel when the clutch was depressed.
 
SUMMARY:
Complaint Owner stated that the transmission was stuck in first or reverse.
Cause Seized pilot bushing.
Correction Replacement of the bushing corrected the stuck in gear concern.
 
The Case of the Worn Shift Fork
A 2007 BMW 325i (113,000 mi) had a problem of firstgear jump-out. The transmission was removed and rebuilt, and a new 1–2 guide sleeve and first gear was installed along with new transmission mounts and rubber shifter mounts. But, this did not fix the problem. When the transmission was disassembled again, the shift fork was measured for wear. The shift fork measured at 0.145 to 0.170 inch, and the dimension of a new fork was 0.190 inch. Replacement of the fork fixed this transmission.
 
SUMMARY:
Complaint Customer complained that the transmission would jump out of first gear.
Cause Worn shift fork.
Correction A replacement shift fork corrected the customer concern.
 
The “Steering Problem” That Was a Drive Axle Problem
A Honda CRV (All-wheel-drive) (130,000 mi) had an objectionable noise while turning. The vehicle owner complained that the problem must be in the power steering system because it only occurred when turning. An inspection of the power steering showed no problem. On a road test, the noise seemed to be coming from the rear so the rear driveshaft was removed, and the noise disappeared. The fluid was drained from the rear drive axle and replaced using the recommended oil, and this fixed this noise problem.
 
SUMMARY:
Complaint Driver complained about a nose while turning.
Cause The rear drive axle was found to be the source of the noise.
Correction The drive axle fluid was replaced with the specified fluid and the noise concern was corrected.
 
The Squeaking Pickup Truck
The owner of a pickup truck complained that a squeaking noise occurred while driving in reverse. The “eeee eeee eeee” sound increased in frequency as the truck increased in speed, yet the noise did not occur when driving forward. Because there was no apparent looseness in the U-joints, the service technician at first thought that the problem was inside either the transmission or the rear end. When the driveshaft was removed to further investigate the problem, it became obvious where the noise was coming from. The U-joint needle bearing had worn the cross-shaft bearing surface of the U-joint.
The noise occurred only in reverse because the wear had occurred in the forward direction, and therefore only when the torque was applied in the opposite direction did the needle bearing become bound up and start to make noise. A replacement U-joint solved the squeaking noise in reverse.
 
SUMMARY:
Complaint Customer complained of squeaking sound but only while driving in reverse.
Cause A worn U-joint was found to be the cause.
Correction The worn U-joint was replaced and the noise issue was corrected.
 
The Vibrating Buick
The owner of a front-wheel-drive Buick complained that it vibrated during acceleration only. The vehicle would also pull toward one side during acceleration. An inspection discovered a worn (cracked) engine mount. After replacing the mount, the CV joint angles were restored and both the vibration and the pulling to one side during acceleration were solved.
 
SUMMARY:
Complaint Owner complained about a vibration and a pull to one side during acceleration.
Cause A defective engine mount which caused the CV joint angles to be unequal causing the vibration and pulling during acceleration.
Correction The engine mount was replaced and the customer concern was solved.
 
The Vibrating Van
After the engine was replaced in a rear-wheel-drive van, a vibration that felt like an engine misfire was noticed by the driver. Because the vibration was not noticed before the engine was replaced, the problem was thought to be engine-related. Many tests failed to find anything wrong with the engine. After hours of troubleshooting, a collapsed transmission mount was discovered. After replacing the transmission mount, the “engine miss” and the vibration were eliminated. The collapsed mount caused the driveshaft U-joint angles to be unequal, which caused the vibration.
 
SUMMARY:
Complaint Customer complained of an engine misfire during acceleration.
Cause A collapsed transmission mount caused the drive shaft U-joint angles to be unequal creating the vibration that was thought to be a misfire.
Correction Both engine mounts were replaced.
 
The Vibrating Van
After the engine was replaced in a rear-wheel-drive van, a vibration that felt like an engine miss was noticed by the driver. Because the vibration was not noticed before the engine was replaced, the problem was thought to be engine-related. Many tests failed to find anything wrong with the engine. Even the ignition distributor was replaced, along with the electronic ignition module, on the suspicion that an ignition misfire was the cause. After hours of troubleshooting, a collapsed transmission mount was discovered. After replacing the transmission mount, the “engine miss” and the vibration were eliminated. The collapsed mount caused the driveshaft U-joint angles to be unequal, which caused the vibration.
 
SUMMARY:
Complaint Owner complained of a vibration during acceleration only that was believed to be an ignition misfire.
Cause The transmission mount was found to have collapsed which affected the drive shaft angles.
Correction The transmission mount was replaced which restored the proper drive shaft angles.
 
The Worn Shift Fork Mystery
A vehicle equipped with a manual transmission had to be repaired several times for worn shift forks. Even though the vehicle warranty paid for the repair, both the customer and the service department personnel were concerned about the repeated failures. All technical service bulletins (TSBs) were checked to see if there was an updated, improved shift fork. No luck. After the third repair, the service technician rode with the customer to see if the cause could be determined. As the woman driver got into the driver’s seat, she placed the handle of her purse over the shifter on the floor and allowed the purse to hang from the shifter. The technician asked the owner if she always placed her purse on the shifter and when she said yes, the technician knew immediately the cause of the worn shift forks. The purse exerted a force on the shifter all the time. This force pushed the shift forks against the synchronizer sleeve. Because the sleeve rotates all the time the vehicle is in motion, the shift forks were quickly worn. The customer agreed to find another location for her purse so that the transmission problem would not reoccur.
 
SUMMARY:
Complaint Repeated manual transmission shift fork failures.
Cause Driver hung her purse over the shifter which exerted a force on the shift forks.
Correction Driver agreed to find another location for her purse.
 

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Bump Steer
Bump steer, or orbital steer, is used to describe what happens when the steering linkage is not level: The front tires turn inward or outward as the wheels and suspension move up and down. (Automotive chassis engineers call it roll steer.) The vehicle’s direction is changed without moving the steering wheel whenever the tires move up and down over bumps, dips in the pavement, or even over gentle rises! This author experienced bump steer once and will never forget the horrible feeling of not having control of the vehicle. After replacing an idler arm and aligning the front wheels, everything was normal until about 40 mph (65 km/h); then the vehicle started darting from one lane of the freeway to another. Because there were no “bumps” as such, bump steer was not considered as a cause. Even when holding the steering wheel perfectly still and straight ahead, the vehicle would go left, then right. Did a tie rod break? It certainly felt exactly like that’s what happened. I slowed down to below 30 mph and returned to the shop. After several hours of checking everything, including the alignment, discovered that the idler arm was not level with the pitman arm. This caused a pull on the steering linkage whenever the suspension moved up and down. As the suspension compressed, the steering linkage pulled inward on the tie rod on that side of the vehicle. As the wheel moved inward (toed in), it created a pull just as if the wheel were turned by the driver. This is why all steering linkages must be parallel with the lower control. The reason for the bump steer was that the idler arm was bolted to the frame, which was slotted vertically. I didn’t pay any attention to the location of the original idler arm and simply bolted the replacement to the frame. After raising the idler arm back up where it belonged (about 1/2 inch [13 mm]), the steering problem was corrected. Other common causes of bump steer are worn or deteriorated rack mounting bushings, a noncentered steering linkage, or a bent steering linkage. If the steering components are not level, any bump or dip in the road will cause the vehicle to steer one direction or the other.
 
SUMMARY:
Complaint Driver complained that the vehicle pulled to one lane and then the other when driving over a rough section of road.
Cause The idler arm was not installed in the correct location to prevent bump steer.
Correction The idler arm was installed correctly and the bump steer was corrected.
 
Everything Is OK until I Hit a Bump
The owner of an eight-year-old vehicle asked that the vibration in the steering wheel be repaired. It seemed that the vehicle drove fine until the front wheels hit a bump in the road—then the steering wheel shimmied for a few seconds. This problem is typical of a vehicle with excessive steering linkage freeplay. When driving straight, centrifugal (rolling) force on the tires tends to force the front wheels outward (toe-out). When one or both wheels hit a bump, the play in the linkage becomes apparent, causing the steering wheel to shimmy until the rolling force again equalizes the steering. The service technician performed a test-drive and a careful steering system inspection and discovered freeplay in both inner tie rod end sockets of the rack-and-pinion unit. The steering unit also had some power steering leakage at the tie rod bellows. A replacement remanufactured power-rack-and pinion steering unit was recommended to the customer. The customer approved the replacement rack and authorized the required realignment. A careful test-drive confirmed that the problem was corrected.
 
SUMMARY:
Complaint Owner complained of vibration but only after hitting a bump in the road.
Cause The rack-and-pinion steering had excessive looseness in both the inner and outer tie rods.
Correction The steering gear assembly was replaced and the problem was corrected.
 
I Thought the Lug Nuts Were Tight!
Proper wheel nut torque is critical, as one technician discovered when a customer returned complaining of a lot of noise from the right rear wheel. The lug (wheel) nuts had loosened and ruined the wheel.
Caution: Most vehicle manufacturers also specify that the wheel studs/nuts should not be lubricated with oil or grease. The use of a lubricant on the threads could cause the lug nuts to loosen.
 
SUMMARY:
Complaint Customer complained of a lot of noise from the rear of the vehicle after a routine tire rotation.
Cause The service technician got distracted when installing the wheels during a tire rotation and forgot to properly torque the lug nuts.
Correction A new wheel was used and the tire mounted and balanced and properly installed. The technician learned to always keep focused on the job being performed.
 
Left Thrust Line, but a Pull to the Right!
A new four-door sport sedan had been aligned several times at the dealership in an attempt to solve a pull to the right. The car had front-wheel-drive and four-wheel independent suspension. The dealer rotated the tires, and it made no difference. The alignment angles of all four wheels were in the center of specifications. The dealer even switched all four tires from another car in an attempt to solve the problem. In frustration, the owner took the car to an alignment shop. Almost immediately the alignment technician discovered that the right rear wheel was slightly toed-in. This caused a pull to the right.
The alignment technician adjusted the toe on the right rear wheel and reset the front toe. The car drove beautifully. The owner was puzzled about why the new car dealer was unable to correct the problem. It was later discovered that the alignment machine at the dealership was out of calibration by the exact amount that the right rear wheel was out of specification. The car pulled to the right because the independent suspension created a rear steering force toward the left that caused the front to pull to the right. Alignment equipment manufacturers recommend that alignment equipment be calibrated regularly.
 
SUMMARY:
Complaint Owner complained that the vehicle pulled to the right after an alignment.
Cause The rear toe on the right was toed in and out of specification.
Correction The technician adjusted the rear toe on the right rear to factory specifications.
 
Strange Leakage
The owner of a small business drove the company pickup truck into the shop to get it ready to load for the day’s delivery. It was a very cold day in northern Ohio with the temperature well below freezing (32ºF (0ºC)). After about 15 minutes, the business owner noticed that “something” was leaking from underneath the rear of the truck. Not sure what it was, the owner called a local automotive repair shop and asked for help. The shop sent a technician to look at the truck. The service technician noticed that one of the rear shock absorbers had leaked all of the hydraulic fluid out of the bottom of the shock.
Obviously, both rear shock absorbers would require replacement because shocks should always be replaced in pairs. The service technician recommended that all four (both front and both rear) shocks be replaced to restore proper handling. Knowing that the front shock absorbers were operating under the same conditions as the rear and were the same age, the truck owner approved the replacement of all four shock absorbers.
 
SUMMARY:
Complaint A liquid was found leaking from underneath a truck.
Cause Hydraulic fluid had leaked from a rusty shock absorber.
Correction Based on the owner’s approval, all four shocks were replaced.
 
The Acura Dash Display Problem
The tires were rotated on an Acura equipped with a direct-type TPMS. The published relearn procedure included driving the vehicle above 15 MPH for at least 40 seconds. However, even after driving for over 10 miles, the pressures were not being displayed on the instrument panel cluster (IPC). The technician thought that maybe there was fault with the IPC. The owner decided to think it over what to do and drove the vehicle home. The next day, when the vehicle was driven, the tire pressure display worked as designed. Apparently the system needed to be powered down and allowed to go to sleep before it would start to transmit the new locations to the IPC.
 
SUMMARY:
Complaint The tire pressures for each wheel were not being displayed on the dash after the tires were rotated.
Cause The tire-pressure monitoring system apparently needed to go to sleep and then awaken before the tire pressure would be displayed on the dash.
Correction No action was required by the service technician because the system started to transmit after going to sleep, and the display operated as designed.
 
The Five-Wheel Alignment
The steering wheel should always be straight when driving on a straight, level road. If the steering wheel is not straight, the customer will often think that the wheel alignment is not correct. One such customer complained that the vehicle pulled to the right while driving on a straight road. The service manager testdrove the vehicle and everything was perfect, except that the steering wheel was not perfectly straight, even though the toe setting was correct. Whenever driving on a straight road, the customer would “straighten the steering wheel” and, of course, the vehicle went to one side. After adjusting toe with the steering wheel straight, the customer and the service manager were both satisfied. The technician learned that regardless of how accurate the alignment, the steering wheel must be straight; it is the “fifth wheel” that the customer notices most. Therefore, a five-wheel alignment rule includes a check of the steering wheel.
Note: Many vehicle manufactures now include the maximum allowable steering wheel angle variation from straight. This specification is commonly ±3 degrees (plus or minus 3 degrees) or less.
 
SUMMARY:
Complaint Owner complained that the vehicle pulled to one side after an alignment.
Cause The steering wheel was not perfectly straight and when the driver straightened the wheel, it went to one side.
Correction The technician straightened the steering using the tie rod end ends while maintaining the specified toe setting.
 
The Hard Steering Chevrolet HHR
The owner of a Chevrolet HHR complained that the steering wheel was harder to turn after the battery was jump started. The tow truck driver did not know what to do and advised the owner to take it to a shop to have it looked at but the driver did not think that jump starting the vehicle could affect the power steering. A technician at the shop determined that the electric power steering did not work because of a blown fuse. Apparently, the vehicle was jump started by connecting the positive jump cable to the main terminal toward the rear of the engine compartment instead of the terminal designed to be used to jump start the vehicle as the battery is located at the rear of this vehicle.
After the blown fuse was replaced, the electric power steering worked correctly.
 
SUMMARY:
Complaint Owner complained that the steering felt stiff after the vehicle was jump started.
Cause The jump start cables were connected to the wrong terminal which caused the fuse to blow that controlled the electric power steering.
Correction The blown fuse was replaced and the power steering system operation was restored to normal.
 
The Harsh Riding Buick
The owner requested that all of the shock absorbers be replaced on a ten-year-old Buick. The rear was equipped with air shocks as part of the ride leveling system. During a test-drive after installing all four shocks, the service technician noticed that it seemed to ride much harsher than normal for a Buick. The technician asked the owner to ride along to verify that it was not usual to ride as harsh as it was. Puzzled as to why this occurred, the technician contacted the parts store which then asked their supplier about the issue. It was discovered that the air shocks were not cycled before they were installed. Installing air shocks/struts requires cycling the shock/strut to spread lubricant inside the diaphragm to avoid binding. The installing technician should inflate the air diaphragm through the air fitting until the shock/strut fully extends. Then the shock can be kept fully extended to make it easier to install. After removing the rear shocks and inflating them as instructed, and reinstalling, the Buick rode normally.
 
SUMMARY:
Complaint The service technician was concerned that the Buick rode harsher than normal after new shock absorbers were installed.
Cause The proper installation procedure was not followed prior to installing the air shock on the rear.
Correction The air shocks were removed and cycled and then inflated before being reinstalled which solved the harsh ride concern.
 
The Noisy Power Steering Pump
A customer complained that the power steering on their Dodge Grand Caravan minivan had a very loud whining/growling/squealing noise for about 3-10 seconds on cold mornings at start-up. The owner had received a quote for several hundred dollars to replace the power steering pump, but then asked another shop for a second opinion. The second shop had experience with this issue and recommended replacing the power steering filter located in the bottom of the power steering pump reservoir. The owner agreed to have the filter and the fluid replaced for an amount far less than the previous quote. After replacing the filter and flushing the power steering fluid, the power steering was quiet and operated like new.
 
SUMMARY:
Complaint Power steering was noisy especially when cold.
Cause The screen in the bottom of the reservoir plugs up and starves the pump of oil causing the noise.
Correction The filter was replaced and the fluid flushed.
 
The Rattle Story
A customer complained that a rattle was heard every time the vehicle hit a bump. The noise sounded as if it came from the rear. All parts of the exhaust system and suspension system were checked. Everything seemed okay until the vehicle was raised with a frame-type hoist instead of a drive-on type. Then, whenever the right rear wheel was lifted, the noise occurred. The problem was a worn (elongated) shock absorber mounting hole. A washer with the propersize hole was welded over the worn lower frame mount and the shock absorber was bolted back into place.
 
SUMMARY:
Complaint Vehicle owner complained of a rattle sound from the rear suspension at times.
Cause The lower shock mount was found to be worn (elongated) causing the noise.
Correction A steel washer was welded over the worn lower frame mount which restored the shock mount to the correct size and solved the noise issue.
 
The Rock-Hard Problem
The owner of a six-month-old full-size pickup truck complained that occasionally when the truck was driven up into a driveway, a loud grinding sound was heard. Several service technicians worked on the truck, trying to find the cause for the noise. After the left front shock absorber was replaced, the noise did not occur for two weeks and then started again. Finally, the service manager told the technician to replace anything and everything in the front suspension in an attempt to solve the customer’s intermittent problem. Five minutes later, a technician handed the service manager a small, deformed rock. This technician had taken a few minutes to carefully inspect the entire front suspension. Around the bottom coil spring seat, the technician found the rock. Apparently, when the truck made a turn over a bump, the rock was forced between the coils of the coil spring, making a very loud grinding noise. But the rock did not always get between the coils. Therefore, the problem occurred only once in a while. The technician handed the rock to the very happy customer.
 
SUMMARY:
Complaint Vehicle owner complained of loud grinding sound from the front suspension at times.
Cause A rock was found at the bottom of the coil spring seat.
Correction The rock was removed.
 
The TPMS Warning Lamp
The owner of a six-year-old Honda Civic was concerned that the tire-pressure warning lamp was on even though all of the tires had the proper inflation pressure. The technician noted that the TPMS warning lamp was not the one that indicates a low tire, but it was the one that indicates that a fault with the system has been detected.
The technician used a factory-level aftermarket scan tool and retrieved several diagnostic trouble codes for “pressure sensor signal failures.”
The technician also noted that the tires were relatively new and recommended to the owner that all four TPMS sensors be replaced. The major reason why the technician recommended that all of them be replaced is that the battery life is normally 7 to 10 years so the life of the sensors is near the end of their useful life. Also, the technician thought that one or more of the sensors may have been damaged when the new tires were replaced. The vehicle owner approved the replacement of the sensors and the system was restored to normal operation.
 
SUMMARY:
Complaint TPMS warning lamp was on.
Cause Most of the tire-pressure warning system sensors had a stored diagnostic trouble code.
Correction All four tire-pressure sensors were replaced and the system relearned to the new sensors. The codes were cleared and the system was restored to normal operation.
 
The Vibrating Ford Van
A technician was asked to solve a vibration problem on a rear-wheel-drive Ford van. During a test-drive, the vibration was felt everywhere—the dash, the steering wheel, the front seat, the shoulder belts; everything was vibrating! The technician balanced all four tires on a computer balancer. Even though wheel weights were put on all four wheels and tires, the vibration was even worse than before. The technician rebalanced all four wheels time after time, but the vibration was still present. The shop supervisor then took over the job of solving the mystery of the vibrating van. The supervisor balanced one wheel/ tire assembly and then tested it again after installing the weights. The balance was way off! The supervisor broke the tire down and found about 1 quart (1 liter) of liquid in each tire! No wonder the tires couldn’t be balanced! Every time the tire stopped, the liquid would settle in another location. The customer later admitted to using a tire stop-leak liquid in all four tires. Besides stop leak, another common source of liquid in tires is water that accumulates in the storage tank of air compressors, which often gets pumped into tires when air is being added. All air compressor storage tanks should be drained of water regularly to prevent this from happening.
 
SUMMARY:
Complaint Customer complained of a vibration.
Cause The technician found stop leak liquid in all four tires.
Correction The stop leak was removed from all the tires and then they were rebalanced. The vibration issues were corrected.
Caution: Stop leak should never be used in a tire that is equipped with the TPMS sensor because the sensor can be damaged.
 
Tire Date Code Information Saved Me Money!
This author was looking at a three-year-old vehicle when I noticed that the right rear tire had a build date code newer than the vehicle. I asked the owner, “How badly was this vehicle hit?” The owner stumbled and stuttered a little, then said, “How did you know that an accident occurred?” I told the owner that the right rear tire, while the exact same tire as the others, had a date code indicating that it was only one year old, whereas the original tires were the same age as the vehicle. The last three numbers of the DOT code on the sidewall indicate the week of manufacture (the first two numbers of the three-digit date code) followed by the last number of the year. The owner immediately admitted that the vehicle slid on ice and hit a curb, damaging the right rear tire and wheel. Both the tire and wheel were replaced and the alignment checked. The owner then dropped the price of the vehicle $500! Knowing the date code helps assure that fresh tires are purchased and can also help the technician determine if the tires have been replaced. For example, if new tires are found on a vehicle with 20,000 miles, then the technician should check to see if the vehicle may have been involved in an accident or may have more miles than indicated on the odometer.
 
SUMMARY:
Complaint Perspective buyer of a used car noticed that one tire was newer than the others.
Cause The owner admitted that the vehicle had slid off the road and hit a curb causing damage to the wheel and tire.
Correction Because the perspective buyer knew the date code, and mentioned this to the seller, the purchase price was reduced saving the buyer money.
 

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Pump to Release?
A customer called and asked a dealer for help because the parking brake could not be released. The service technician discovered that the customer was attempting to release the parking brake by depressing the parking brake pedal, as was done on the customer’s previous vehicle. The service technician simply pulled on the release lever and the parking brake was released.
 
SUMMARY:
Complaint Customer called the service department and asked for help releasing the parking brake as it would not release.
Cause service technician simply pulled on the parking brake release lever to disengage the parking brake.
Correction No repair was needed except to inform the customer that the parking brake on the new vehicle was released using a release lever and not by depressing the foot-operated parking brake pedal as was used in the owner’s previous vehicle.
The Mystery ABS Amber Warning Light
The owner complained to a service technician that the ABS warning light would come on but only while driving down from a parking garage. When the driver turned off the ignition and restarted the engine, the ABS amber light was not on and did not come on again until the vehicle was again driven down the spiral parking garage ramp. The service technician used a scan tool and found that no DTCs had been stored. Note: Some ABS systems will not retain a DTC unless the problem is currently present and the ABS amber warning light is on. All of the brakes were in excellent condition, but the brake fluid level was down a little. After topping off the master cylinder with clean DOT 3 brake fluid, the vehicle was returned to the customer with the following information:
• The ABS amber warning light may have been triggered by the brake fluid level switch. While driving down the steep parking garage ramp, the brake fluid moved away from the fluid level sensor.
Note: While the brake fluid level sensor normally would turn on the red brake warning light, in some systems it turns on the amber ABS light if the brake fluid falls below a certain level in the ABS reservoir.
• The difference in wheel speed between the outboard and the inboard wheels could have triggered a fault code for a wheel speed sensor during the drive down the spiral parking garage ramp.
 
SUMMARY:
Complaint Driver stated that the amber ABS warning lamp would come on but only when descending in a parking garage.
Cause Possible low brake fluid level or normal operation due to change in wheel speed while turning sharply.
Correction Added a slight amount of brake fluid to return the level to the “MAX” level and returned to owner.
 
The Nervous Honda Civic
A customer complained that sometimes during normal braking, the ABS would be activated (brake pedal pulsated) just before coming to a stop. However, the ABS light would not come on. The service technician was able to duplicate the condition and there were no DTCs stored. Using a scan tool to monitor the wheel speed sensors, the technician discovered that the left front wheel speed was slightly different than the others. A thorough visual inspection revealed that the tone wheel (reluctor ring) was cracked. This crack created a different wheel speed signal to the ABS controller than the other wheels and the controller activated the ABS as it would normally—that was why there were no DTCs. Other things that could have caused this problem, which is often called “false modulation,” include a bent wheel, mismatched tire sizes, or metal debris around the sensor
 
SUMMARY:
Complaint Driver complained that the ABS caused the brake pedal to pulsated but only when the vehicle was slowing to a stop.
Cause A cracked tone (reluctor) ring was discovered on the right front.
Correction The customer authorized the replacement of a new wheel bearing assembly which included the tone ring and the problem was corrected.
 
The Noisy Lexus
A customer complained that a noise was heard from the rear of a Lexus RX350 SUV. During a test drive, the service technician did notice a slight noise and thought it might be due to a tire. Driving over various types of road surfaces did not change the level or the pitch (frequency) of the noise indicating that the noise was due to a bearing rather than a tire. As a double check that a tire was not the issue, the technician rotated tires placing the front tires in the rear and the rear tires on the front. Another test drive resulted in the same results. The technician then recommended that the right rear wheel bearing (bearing hub assembly) be replaced and the customer agreed to the estimate. When the hub bearing was removed and checked for any roughness, the technician did not feel or hear any noise from the old bearing. However, once the new bearing was replaced the noise was gone during a test drive.
 
SUMMARY:
Complaint Customer complained of a noise from the right rear of the SUV.
Cause Defective wheel bearing.
Correction Replacing the right rear bearing/hub assembly fixed the noise concern.
 
The Pike’s Peak Brake Inspection
All vehicles must stop about halfway down Pike’s Peak Mountain in Colorado (14,110 ft [4,300 m]) for a “brake inspection.” When this author stopped at the inspection station, a uniformed inspector simply looked at the right front wheel and waved us on. I pulled over and asked the inspector what he was checking. He said that when linings and drums/rotors get hot, the vehicle loses brake effectiveness. But if the brake fluid boils, the vehicle loses its brakes entirely. The inspector was listening for boiling brake fluid at the front wheel and feeling for heat about 1 ft (30 cm) from the wheel. The inspector used an infrared pyrometer to measure the front wheel brakes and if the brakes were too hot to continue, you would be instructed to pull over and wait for the brakes to cool. The inspector recommended placing the transmission into a lower gear, which uses the engine to slow the vehicle during the descent without having to rely entirely on the brakes.
 
SUMMARY:
Complaint Vehicle was stopped for an inspection.
Cause If the brakes are too hot, the brake fluid can boil and as a result a total loss of brakes is likely.
Correction Informed driver that this is normal procedure and a safety precaution.
 
The Sinking Brake Pedal
This author has experienced what happens when brake fluid is not changed regularly. Just as many technicians will tell you, we do not always do what we know should be done to our own vehicles. While driving a fouryear- old vehicle on vacation in very hot weather in a mountainous country, the brake pedal sank to the floor. When the vehicle was cold, the brakes were fine. But after several brake applications, the pedal became soft and spongy and sank slowly to the floor if pressure was maintained on the brake pedal. Because the brakes were okay when cold, I knew it had to be boiling brake fluid. Old brake fluid (four years old) often has a boiling point under 300°F (150°C). With the air temperature near 100°F (38°C), it does not take much more heat to start boiling the brake fluid. After bleeding over a quart (1 liter) of new brake fluid through the system, the brakes worked normally. I’ll never again forget to replace the brake fluid as recommended by the vehicle manufacturer.
 
SUMMARY:
Complaint Brake pedal would sink to the floor when driving in mountainous country.
Cause The brake fluid was boiling causing the loss of brakes.
Correction The brake fluid was replaced and the system bled.
 
Three Brake Jobs in 40,000 Miles
A service technician was asked to replace the front disc brake pads on a Pontiac Grand Am because the sensors were touching the rotors and making a squealing sound. This was the third time that the front brakes needed to be replaced. Previous brake repairs had been limited to replacement of the front disc brake pads only. When the caliper was removed and the pads inspected, it was discovered that a part of one pad had broken and a piece of the lining was missing. See Figure 13–15 of Automotive Brakes. Then the technician spotted something at the rear of the vehicle that told the whole story—a trailer hitch. The owner confirmed that a heavy jet ski was towed in hilly terrain. The technician recommended overhauling the front disc brake calipers to prevent the possibility of the front pads dragging. The technician also recommended an inspection of the rear brakes. The rear brakes were glazed and out of adjustment. The technician received permission to replace the rear brakes, replace both front calipers, and install quality disc brake pads. When the customer returned, the technician advised the customer to use a lower gear in the transmission on long downhill roads to help keep the brakes from overheating and failing prematurely.
 
SUMMARY:
Complaint The front calipers needed replacement more often than expected.
Cause The front calipers were not retracting and the rear brakes were not working as designed.
Correction Front calipers were replaced and the rear brakes were serviced. Plus the owner was advised to use the gear selector when descending long grades to reduce the load on the brakes.
 
Weird Chevrolet Truck Brakes
The owner of a newer Chevrolet pickup truck complained that sometimes after stopping on a hill, the brakes felt as if the brakes were slow to release when the driver removed his foot from the brake pedal and started to accelerate when the traffic light turned green. The technician was able to duplicate the concern if stopped on a hill either upward or downward. The technician discovered when searching service information that the vehicle was equipped with a hill assist program. This part of the antilock brake system holds the brake applied if the longitudinal acceleration sensor senses that the vehicle was on a hill and the driver exerted a force to the brake pedal to keep the vehicle stopped. Under these conditions, the ABS controller maintained brake fluid pressure in the system to keep the brakes applied until the driver released the brake pedal. What the driver was feeling was the slight delay in the releasing of the brakes when the brake pedal was released.
 
SUMMARY:
Complaint Brakes are slow to release at times.
Cause Normal condition when the vehicle is stopped on a hill when equipped with hill assist.
Correction Informed driver that this is normal operation due to hill assist function.
 

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A Technician's Toughie
The owner of a Honda Civic complained that engine did not run smoothly and the “Check Engine“ light was on. The service technician retrieved a P0300 (random misfire detected) as well as a P0303 ( cylinder number three misfire detected). A scope was connected to each of the coils one at a time and the secondary pattern looked perfect on all four cylinders. All four coils and spark plugs were removed yet they all looked normal. The spark plug for cylinder #3 was moved to cylinder #1 and then the coils were re-installed and the vehicle driven on a test drive. A P0301 was then retrieved which indicated that the problem was due to the spark plug itself. Replacing the spark plug with a new one solved the misfire problem. The plug was apparently cracked yet not seen. The scope showed a normal secondary pattern because the voltage needed to jump to ground through the crack in the plug was about the same as would be required to jump the gap inside the combustion chamber.
 
SUMMARY:  
Complaint Customer stated that the engine ran poorly.
Cause Tests confirmed that one spark plug was found to be cracked.
Correction Replacing the spark plug solved the engine misfire problem.
 
Electronic Devices Cannot Swim
The owner of a Dodge minivan complained that after the vehicle was cleaned inside and outside, the temperature gauge, fuel gauge, and speedometer stopped working. The vehicle speed sensor was checked and found to be supplying a square wave signal that changed with vehicle speed. A scan tool indicated a speed, yet the speedometer displayed zero all the time. Finally, the service technician checked the body control module (BCM) to the right of the accelerator pedal and noticed that it had been wet, from the interior cleaning. Drying the BCM did not fix the problem, but a replacement BCM fixed all the problems. The owner discovered that electronic devices do not like water and that computers cannot swim.
 
SUMMARY:
Complaint Customer complained of many gauges stopped working after the vehicle was cleaned.
Cause The body control module (BCM) was found to be wet and had to be replaced to fix the problems.
Correction Replacing the BCM was needed to fix the problems.
 
Lightning Damage
A radio failed to work in a vehicle that was outside during a thunderstorm. The technician checked the fuses and verified that power was reaching the radio. Then the technician noticed the antenna. It had been struck by lightning. Obviously, the high voltage from the lightning strike traveled to the radio receiver and damaged the circuits. Both the radio and the antenna were replaced to correct the problem.
 
SUMMARY:
Complaint Customer stated that the radio did not work.
Cause Visual inspection showed an antenna that had been stuck by lightning.
Correction Replacing the radio and the antenna restored proper operation.
 
"Oops"
After overhauling a big block Ford V-8 engine, the technician used an electric drill to rotate the oil pump with a pressure gauge connected to the oil pressure sending unit hole. When the electric drill was turned on, oil pressure would start to increase (to about 10 PSI), then drop to zero. In addition, the oil was very aerated (full of air). Replacing the oil pump did not solve the problem. After hours of troubleshooting and disassembly, it was discovered that an oil gallery plug had been left out underneath the intake manifold. The oil pump was working correctly and pumped oil throughout the engine and out of the end of the unplugged oil gallery. It did not take long for the oil pan to empty and the oil pump began drawing in air that aerated the oil which caused the oil pressure to drop. Installing the gallery plug solved the problem.
Note: Many overhead camshaft engines use an oil passage check valve in the block near the deck. The purpose of this valve is to hold oil in the cylinder head around the camshaft and lifters when the engine is stopped. Failure to reinstall this check valve can cause the valve train to be noisy after engine start-up.
 
SUMMARY:  
Complaint Newly overhauled engine lost oil pressure shortly after start up.
Cause An oil gallery plug was found to be missing.
Correction The missing plug was installed and after reassembly, the engine oil pressure was normal.
 
Owner’s Manual Is the Key to Proper Operation
A customer purchased a used Pontiac Vibe and complained to a shop that the cruise control would disengage and had to be reset if driven below 25 mph (40 km/h). The service technician was able to verify that in fact this occurred, but did not know if this feature was normal or not. The technician checked the owner’s manual and discovered that this vehicle was designed to operate this way. Unlike other cruise control systems, those systems on Toyota-based vehicles are designed to shut off below 25 mph, requiring the driver to reset the desired speed. The customer was informed that nothing could be done to correct this concern and the technician also learned
 
SUMMARY:
Complaint The owner of a Ponitiac Vibe complained that the cruise control would stop working if the speed dropped below 25 mph.
Cause The owner’s manual indicated that this is normal operation.
Correction The customer was informed that this is normal operation and that no repair is needed or required.
 
Shocking Experience
A customer complained that after driving for a while, he got a static shock whenever he grabbed the door handle when exiting the vehicle. The customer thought that there must be an electrical fault and that the shock was coming from the vehicle itself. In a way, the shock was caused by the vehicle, but it was not a fault. The service technician sprayed the cloth seats with an antistatic spray and the problem did not reoccur. Obviously, a static charge was being created by the movement of the driver’s clothing on the seats and then discharged when the driver touched the metal door handle.
 
SUMMARY:
Complaint Vehicle owner complained that he got shocked when the door handle was touched.
Cause Static electricity was found to be the cause and not a fault with the vehicle.
Correction The seats and carpet were sprayed with an anti-static spray and this corrected the concern.
 
The Blazer Story
The owner of a Chevrolet Blazer equipped with a 4.3 liter V-6 engine complained that the engine would stumble and hesitate at times. Everything seemed to be functioning correctly, except that the service technician discovered a weak vacuum going to the EGR valve at idle. This vehicle was equipped with an EGR valve-control solenoid, called an electronic vacuum regulator valve (EVRV) by General Motors Corporation. The computer pulses the solenoid to control the vacuum that regulates the operation of the EGR valve. The technician checked the service manual for details on how the system worked. The technician discovered that vacuum should be present at the EGR valve only when the gear selector indicates a drive gear (drive, low, reverse). Because the technician discovered the vacuum at the solenoid to be leaking, the solenoid was obviously defective and required replacement. After replacement of the solenoid (EVRV), the hesitation problem was solved.
 
SUMMARY:  
Complaint Vehicle owner complained that the engine would stumble and hesitate at times.
Cause The EGR vacuum solenoid was found to be leaking.
Correction The EGR solenoid was replaced which restored proper engine operation.
 
The Case of the Haunted Mirrors
The owner complained that while driving either one or the other outside mirror would fold in without any button being depressed. Unable to verify the customer concern, the service technician looked at the owner’s manual to find out exactly how the mirrors were supposed to work. In the manual, a caution statement said that if the mirror is electrically folded inward and then manually pushed out, the mirror will not lock into position. The power folding mirrors must be electrically cycled outward, using the mirror switches to lock them in position. After cycling both mirrors inward and outward electrically, the problem was solved.
 
SUMMARY:
Complaint Customer stated that the outside power folding mirror would fold by itself at times.
Cause The mirrors have to moved electrically and not manually to work correctly.
Correction Cycling the mirrors electrically restored proper operation.
 
The Case of the No Crank
A 4-cylinder engine would not crank. Previously the customer said that once in a while, the starter seemed to lock up when the vehicle sat overnight but would then finally crank. The vehicle finally would not start and was towed to the shop. The service technician checked the current draw of the starter and it read higher than the scale on the ammeter. The technician then attempted to rotate the engine by hand and found that the engine would not rotate. Based on this history of not cranking normally in the morning, the technician removed the spark plugs and attempted to crank the engine. This time the engine cranked and coolant was seen shooting from cylinders 2 and 3. Replacing the bad gasket solved the cranking problems in the morning.
 
SUMMARY:  
Complaint Engine would not crank after sitting overnight.
Cause Blown head gasket caused coolant to enter the cylinder prevent the engine from rotating.
Correction Replacing the head gasket solved the no cranking issue.
 
The Chevrolet Battery Story
A 2011 Chevrolet Impala was being diagnosed for a dead battery. Testing for a battery drain (parasitic draw) showed 2.25 amperes, which was clearly over the acceptable value of 0.050 or less. At the suggestion of the shop foreman, the technician used a Tech 2 scan tool to check if all of the computers and modules went to sleep after the ignition was turned off. The scan tool display indicated that the instrument panel (IP) showed that it remained awake after all of the others had gone into sleep mode. The IP cluster was unplugged and the vehicle was tested for an electrical drain again. This time, it was only 32 milliamperes (0.032 ampere), well within the normal range. Replacing the IP cluster solved the excessive battery drain.
 
SUMMARY:
Complaint The battery was died.
Cause Excessive battery drain (parasitic draw) was found. Using a scan tool to test the modules, it was discovered that the instrument panel cluster (IPC) remained awake and never powered down when the ignition was turned off
Correction The IPC was replaced which corrected the excessive battery drain problem.
 
The Electric Mirror Fault Story
A customer noticed that the electric mirrors stopped working. The service technician checked all electrical components in the vehicle and discovered that the interior lights were also not working. The interior lights were not mentioned by the customer as being a problem most likely because the driver only used the vehicle in daylight hours. The service technician found the interior light and power accessory fuse blown. Replacing the fuse restored the proper operation of the electric outside mirror and the interior lights. However, what caused the fuse to blow? A visual inspection of the dome light, next to the electric sunroof, showed an area where a wire was bare. Evidence showed the bare wire had touched the metal roof, which could cause the fuse to blow. The technician covered the bare wire with a section of vacuum hose and then taped the hose with electrical tape to complete the repair.
 
SUMMARY:
Complaint The electric power mirrors stopped working.
Cause A blown fuse due to a fault in the wiring at the dome light.
Correction Repaired the wiring at the dome light which restored the proper operation of the electric mirrors that shared the same fuse as the dome light.
 
The General Motors Security Radio Problem
A customer replaced the battery in a General Motors vehicle and now the radio display shows “LOC.” This means that the radio is locked and there is a customer code stored in the radio. Other displays and their meaning include:
“InOP” This display indicates that too many incorrect codes have been entered and the radio must be kept powered for one hour and the ignition turned on before any more attempts can be made.
“SEC” This display means there is a customer’s code stored and the radio is unlocked, secured, and operable.
“---” This means there is no customer code stored and the radio is unlocked.
“REP” This means the customer’s code has been entered once and the radio now is asking that the code be repeated to verify it was entered correctly the first time.
To unlock the radio, the technician used the following steps (the code number being used is 4321).
step 1 Press the “HR” (hour) button: “000” is displayed.
step 2 Set the first two digits using the hour button: “4300” is displayed.
step 3 Set the last two digits of the code using the “MIN” (minutes) button: “4321” is displayed.
step 4 Press the AM-FM button to enter the code. The radio is unlocked and the clock displays “1:00.”
Thankfully, the owner had the security code. If the owner had lost the code, the technician would have to secure a scrambled factory backup code from the radio and then call a toll-free number to obtain another code for the customer. The code will only be given to authorized dealers or repair facilities.
 
SUMMARY:
Complaint Customer stated that the radio was locked out after a battery replacement.
Cause Normal operation for radios equipped with security features.
Correction After installing the security code, the radio operation was restored.
 
The Short-to-Voltage Story
A technician was working on a Chevrolet pickup truck with the following unusual electrical problems.
1. When the brake pedal was depressed, the dash light and the side marker lights would light.
2. The turn signals caused all lights to blink and the fuel gauge needle to bounce up and down.
3. When the brake lights were on, the front parking lights also came on. NOTE: Using a single-filament bulb (such as a #1156) in the place of a dual-filament bulb (such as a #1157) could also cause many of these same problems.
Because most of the trouble occurred when the brake pedal was depressed, the technician decided to trace all the wires in the brake light circuit. The technician discovered the problem near the exhaust system. A small hole in the tailpipe (after the muffler) directed hot exhaust gases to the wiring harness containing all of the wires for circuits at the rear of the truck. The heat had melted the insulation and caused most of the wires to touch. Whenever one circuit was activated (such as when the brake pedal was applied), the current had a complete path to several other circuits. A fuse did not blow because there was enough resistance in the circuits being energized, so the current (in amperes) was too low to blow any fuses.
 
SUMMARY:
Complaint Customer stated that the truck lights were doing strange things when the brake pedal was depressed.
Cause Melted wires caused by a small hole in the exhaust was found during a visual inspection.
Correction Performing a wire repair and fixing the exhaust leak corrected the customer concern.
 
The Speedometer Works as if It Is a Tachometer
The owner of a Lincoln Town Car complained that all of a sudden the speedometer needle went up and down with engine speed rather than vehicle speed. In fact, the speedometer needle went up and down with engine speed even though the gear selector was in “park” and the vehicle was not moving. After hours of troubleshooting, the service technician went back and started checking the basics and discovered that the alternator had a bad diode. The technician measured over 1 volt AC and over 10 amperes AC ripple current using a clamp-on AC/DC ammeter. Replacing the alternator restored the proper operation of the speedometer.
 
SUMMARY:
Complaint Customer stated that the speedometer would move in relation to engine speed and not vehicle speed.
Cause Tests confirmed that the alternator was producing excessive AC voltage due to a bad diode.
Correction Replacing the alternator restored proper operation of the speedometer.
 
The Start/Stall/Start/Stall Problem
A Chevrolet 4-cylinder engine would stall every time it was started. The engine cranked normally and the engine started quickly. It would just stall once it had run for about 1 second. After hours of troubleshooting, it was discovered that if the “gages” fuse was removed, the engine would start and run normally. Because the alternator was powered by the “gages” fuse, the charging voltage was checked and found to be over 16 volts just before the engine stalled. Replacing the alternator fixed the problem. The computer shut down to prevent damage when the voltage exceeded 16 volts.
 
SUMMARY:  
Complaint Engine would stall every time it started.
Cause The alternator was over charging causing the PCM to shut off the engine to protect itself against the higherthan- normal voltage.
Correction Replacing the alternator corrected the engine stall after start concern.
 
The Toyota Truck Story
The owner of a Toyota truck complained that several electrical problems plagued the truck, including the following:
1. The cruise (speed) control would kick out intermittently.
2. The red brake warning lamp would come on, especially during cold weather.
An experienced technician checked the wiring diagram in service information. Checking the warning lamp circuit, the technician noticed that the same wire went to the brake fluid level sensor. The brake fluid was at the minimum level. Filling the master cylinder to the maximum level with clean brake fluid solved both problems. The electronics of the cruise control stopped operation when the red brake warning lamp was on as a safety measure.
 
SUMMARY:
Complaint Customer stated that the truck had a couple of electrical problems.
Cause Visual inspection found that the brake fluid was low triggering the red brake warning light and the cruise control.
Correction Adding some brake fluid restored proper operation of the electrical system.
 
The Two Minute Alternator Repair
A Chevrolet pickup truck was brought to a dealer for routine service. The owner stated that the battery required a jump start after a weekend of sitting. The technician tested the battery and charging system voltage using a small handheld digital multimeter. The battery voltage was 12.4 volts (about 75% charged), but the charging voltage was also 12.4 volts at 2000 RPM. Because normal charging voltage should be 13.5 to 15 volts, it was obvious that the charging system was not operating correctly. The technician checked the dash and found that the “charge” light was not on. Before removing the alternator for service, the technician checked the wiring connection on the alternator. When the lead regulator connector was removed, the connector was discovered to be rusty. After the contacts were cleaned, the charging system was restored to normal operation. The technician had learned that the simple things should always be checked first before tearing into a big (or expensive) repair.
 
SUMMARY:  
Complaint Battery was dead after sitting over the weekend.
Cause The alternator was not charging due to a poor electrical connection at the alternator.
Correction The electrical connector was cleaned and the charging system was restored to normal operation.
 
The Weird Running Chevrolet Truck
An older Chevrolet pickup truck equipped with a V-8 engine was towed into a shop because it would not start. A quick check of the ignition system showed that the pickup coil had a broken wire below it and the ignition control module. The distributor was removed from the engine and the distributor shaft was removed, cleaned, and a replacement pickup coil was installed. The engine started but ran rough and hesitated when the accelerator pedal was depressed. After an hour of troubleshooting, a careful inspection of the new pickup coil showed that the time core had six instead of eight points, meaning that the new pickup coil was meant for a V-6 instead of a V-8 engine. Replacing the pickup coil again solved the problem.
 
SUMMARY:  
Complaint Customer stated that the truck would not start.
Cause A visual inspection was used to determine a that a pickup coil wire was broken and was replaced but with the wrong part that was in the correct box.
Correction Replacing the pickup coil with the right part fixed the truck.
 
Weird Problem—Easy Solution
A General Motors minivan had the following electrical problems.
• The turn signals flashed rapidly on the left side.
• With the ignition key off, the lights-on warning chime sounded if the brake pedal was depressed.
• When the brake pedal was depressed, the dome light came on.
All of these problems were caused by one defective 2057 dual-filament bulb, as shown in
Apparently, the two filaments were electrically connected when one filament broke and then welded to the other filament. This caused the electrical current to feed back from the brake light filament into the taillight circuit, causing all the problems.
 
SUMMARY:
Complaint Customer stated that there were many electrical problems.
Cause A defective bulb was found during a visual inspection.
Correction Replacing the bulb corrected all of the electrical-related issues.
 

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Cabin Filter Fault
The owner of a Ford Escape complained that the airconditioning system was not cooling the inside of the vehicle and there seemed to be no airflow from the dash vents yet the blower motor could be heard running. A quick visual inspection of the cabin air filter with access under the hood showed that the cabin filter was almost completely blocked with paper, leaves, and debris. The vehicle had almost 80,000 miles on the odometer and the way it looked, the air filter had never been replaced. Most vehicle manufacturers recommend replacement of the cabin air filter about every three years or every 36,000 miles. Replacing the cabin air filter restored proper operation of the A/C system.
 
SUMMARY:
Complaint Customer complained of a lack of airflow from the dash vents.
Cause A partially clogged cabin filter.
Correction Replacement of the cabin filter restored proper airflow from the dash vents.
 
The Collapsed Radiator Hose Story
An automotive student asked the automotive instructor what brand of radiator hose is the best. Not knowing exactly what to say, the instructor asked if there was a problem with the brand hose used. The student had tried three brands and all of them collapsed when the engine cooled. The instructor then explained that the vehicle needed a new pressure cap and not a new upper radiator hose. The student thought that because the lower hose did not collapse that the problem had to be a fault with the hose. The instructor then explained that the lower radiator hose has a spring inside to keep the lower hose from collapsing due to the lower pressure created at the inlet to the water pump. The radiator cap was replaced and the upper radiator hose did not collapse when the engine cooled.
 
SUMMARY:  
Complaint Vehicle owner stated the upper radiator hose would collapse when the engine cools.
Cause The upper radiator collapsed due to a fault with the radiator pressure cap.
Correction A new radiator cap solved the problem.
 
Highway Overheating
A vehicle owner complained of an overheating vehicle, but the problem occurred only while driving at highway speeds. The vehicle, equipped with a 4-cylinder engine, would run in a perfectly normal manner in city driving situations. The technician flushed the cooling system and replaced the radiator cap and the water pump, thinking that restricted coolant flow was the cause of the problem. Further testing revealed coolant spray out of one cylinder when the engine was turned over by the starter with the spark plugs removed. A new head gasket solved the problem. Obviously, the head gasket leak was not great enough to cause any problems until the engine speed and load created enough flow and heat to cause the coolant temperature to soar. The technician also replaced the oxygen (O2)sensor.
 
SUMMARY:  
Complaint Customer stated that the engine would overheat but only if driven at highway speed.
Cause The root cause was determined to be a defective head gasket.
Correction The head gasket was replaced and the oxygen sensor was also replaced because coolant can cause the sensor to read incorrectly. Replacing the oxygen sensor was done to be insured that the engine ran correctly.
 

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A Technician's Toughie
The owner of a Honda Civic complained that engine did not run smoothly and the “Check Engine“ light was on. The service technician retrieved a P0300 (random misfire detected) as well as a P0303 ( cylinder number three misfire detected). A scope was connected to each of the coils one at a time and the secondary pattern looked perfect on all four cylinders. All four coils and spark plugs were removed yet they all looked normal. The spark plug for cylinder #3 was moved to cylinder #1 and then the coils were re-installed and the vehicle driven on a test drive. A P0301 was then retrieved which indicated that the problem was due to the spark plug itself. Replacing the spark plug with a new one solved the misfire problem. The plug was apparently cracked yet not seen. The scope showed a normal secondary pattern because the voltage needed to jump to ground through the crack in the plug was about the same as would be required to jump the gap inside the combustion chamber.
 
SUMMARY:  
Complaint Customer stated that the engine ran poorly.
Cause Tests confirmed that one spark plug was found to be cracked.
Correction Replacing the spark plug solved the engine misfire problem.
 
Big Problem, No Noise
Sometimes the piston pin can “walk” off the center of the piston and score the cylinder wall. This scoring is often not noticed because this type of wear does not create noise. Because the piston pin is below the piston rings, little combustion pressure is lost past the rings until the groove worn by the piston pin has worn the piston rings. Troubleshooting the exact cause of the increased oil consumption is difficult because the damage done to the oil control rings by the groove usually affects only one cylinder. Often, compression tests indicate good compression because of the cylinder seals, especially at the top. More than one technician has been surprised to see the cylinder gouged by a piston pin when the cylinder head has been removed for service. In such a case, the cost of the engine repair immediately increases far beyond that of normal cylinder head service.
 
SUMMARY:  
Complaint Engine was burning oil yet the compression was good leading the technician to remove the head.
Cause A piston pin had moved and scored the cylinder wall.
Correction The engine was replaced to correct the oil burning concern.
 
Highway Overheating
A vehicle owner complained of an overheating vehicle, but the problem occurred only while driving at highway speeds. The vehicle, equipped with a 4-cylinder engine, would run in a perfectly normal manner in city driving situations. The technician flushed the cooling system and replaced the radiator cap and the water pump, thinking that restricted coolant flow was the cause of the problem. Further testing revealed coolant spray out of one cylinder when the engine was turned over by the starter with the spark plugs removed. A new head gasket solved the problem. Obviously, the head gasket leak was not great enough to cause any problems until the engine speed and load created enough flow and heat to cause the coolant temperature to soar. The technician also replaced the oxygen (O2)sensor.
 
SUMMARY:  
Complaint Customer stated that the engine would overheat but only if driven at highway speed.
Cause The root cause was determined to be a defective head gasket.
Correction The head gasket was replaced and the oxygen sensor was also replaced because coolant can cause the sensor to read incorrectly. Replacing the oxygen sensor was done to be insured that the engine ran correctly.
 
If 50% Is Good, 100% Must Be Better
A vehicle owner said that the cooling system of his vehicle would never freeze or rust. He said that he used 100% antifreeze (ethylene glycol) instead of a 50/50 mixture with water. However, after the temperature dropped to −20°F (−29°C), the radiator froze and cracked. (Pure antifreeze freezes at about 0°F [−18°C].) After thawing, the radiator had to be replaced. The owner was lucky that the engine block did not also crack. For best freeze protection with good heat transfer, use a 50/50 mixture of antifreeze and water. As the percentage of antifreeze increases, the boiling temperature increases, and freezing protection increases (up to 70% antifreeze), but the heat transfer performance of the mixture decreases.
 
SUMMARY:  
Complaint The coolant froze and cracked the radiator.
Cause Vehicle owner used 100% antifreeze instead of the recommended 50/50 mixture of antifreeze and water.
Correction The radiator was replaced and the proper mixture of antifreeze/water was used as the coolant.
 
O2S Shows Rich, But Pulse Width Is Low
A service technician was attempting to solve a driveability problem. The computer did not indicate any diagnostic trouble codes (DTCs). A check of the oxygen sensor voltage indicated a higher-thannormal reading almost all the time. The pulse width to the port injectors was lower than normal. The lowerthan-normal pulse width indicates that the computer is attempting to reduce fuel flow into the engine by decreasing the amount of on-time for all the injectors. What could cause a rich mixture if the injectors were being commanded to deliver a lean mixture? Finally the technician shut off the engine and took a careful look at the entire fuel-injection system. When the vacuum hose was removed from the fuel-pressure regulator, fuel was found dripping from the vacuum hose. The problem was a defective fuel-pressure regulator that allowed an uncontrolled amount of fuel to be drawn by the intake manifold vacuum into the cylinders. While the computer tried to reduce fuel by reducing the pulse width signal to the injectors, the extra fuel being drawn directly from the fuel rail caused the engine to operate with too rich an air–fuel mixture.
 
SUMMARY:
Complaint Customer stated that the engine did not perform correctly.
Cause No stored diagnostic trouble codes (DTCs) were found but the oxygen sensor reading was higher than normal indicating that the exhaust air-fuel mixture was too rich.
Correction The fuel pressure regulator was found to be leaking causing fuel to be drawn into the intake causing the richer- then-normal air-fuel mixture. Replacing the fuel pressure regulator solved the driveability complaint.
 
"Oops"
After overhauling a big block Ford V-8 engine, the technician used an electric drill to rotate the oil pump with a pressure gauge connected to the oil pressure sending unit hole. When the electric drill was turned on, oil pressure would start to increase (to about 10 PSI), then drop to zero. In addition, the oil was very aerated (full of air). Replacing the oil pump did not solve the problem. After hours of troubleshooting and disassembly, it was discovered that an oil gallery plug had been left out underneath the intake manifold. The oil pump was working correctly and pumped oil throughout the engine and out of the end of the unplugged oil gallery. It did not take long for the oil pan to empty and the oil pump began drawing in air that aerated the oil which caused the oil pressure to drop. Installing the gallery plug solved the problem.
Note: Many overhead camshaft engines use an oil passage check valve in the block near the deck. The purpose of this valve is to hold oil in the cylinder head around the camshaft and lifters when the engine is stopped. Failure to reinstall this check valve can cause the valve train to be noisy after engine start-up.
 
SUMMARY:  
Complaint Newly overhauled engine lost oil pressure shortly after start up.
Cause An oil gallery plug was found to be missing.
Correction The missing plug was installed and after reassembly, the engine oil pressure was normal.
 
The Blazer Story
The owner of a Chevrolet Blazer equipped with a 4.3 liter V-6 engine complained that the engine would stumble and hesitate at times. Everything seemed to be functioning correctly, except that the service technician discovered a weak vacuum going to the EGR valve at idle. This vehicle was equipped with an EGR valve-control solenoid, called an electronic vacuum regulator valve (EVRV) by General Motors Corporation. The computer pulses the solenoid to control the vacuum that regulates the operation of the EGR valve. The technician checked the service manual for details on how the system worked. The technician discovered that vacuum should be present at the EGR valve only when the gear selector indicates a drive gear (drive, low, reverse). Because the technician discovered the vacuum at the solenoid to be leaking, the solenoid was obviously defective and required replacement. After replacement of the solenoid (EVRV), the hesitation problem was solved.
 
SUMMARY:  
Complaint Vehicle owner complained that the engine would stumble and hesitate at times.
Cause The EGR vacuum solenoid was found to be leaking.
Correction The EGR solenoid was replaced which restored proper engine operation.
 
The Case of the No Crank
A 4-cylinder engine would not crank. Previously the customer said that once in a while, the starter seemed to lock up when the vehicle sat overnight but would then finally crank. The vehicle finally would not start and was towed to the shop. The service technician checked the current draw of the starter and it read higher than the scale on the ammeter. The technician then attempted to rotate the engine by hand and found that the engine would not rotate. Based on this history of not cranking normally in the morning, the technician removed the spark plugs and attempted to crank the engine. This time the engine cranked and coolant was seen shooting from cylinders 2 and 3. Replacing the bad gasket solved the cranking problems in the morning.
 
SUMMARY:  
Complaint Engine would not crank after sitting overnight.
Cause Blown head gasket caused coolant to enter the cylinder prevent the engine from rotating.
Correction Replacing the head gasket solved the no cranking issue.
 
The Case of the Wrong Oil
A 2007 Dodge Durango was in the shop for routine service, including a tire rotation and an oil change. Shortly after, the customer returned and stated that the “check engine” light was on. A scan tool was used to retrieve any diagnostic trouble codes. A P0521, “oil pressure not reaching specified value at 1250 RPM” was set. A check of service information showed that this code could be set if the incorrect viscosity engine oil was used. The shop had used SAE 10W-30 but the 5.7 liter Hemi V-8 with multiple displacement system (MDS) required SAE 5W-20 oil. The correct oil was installed and the DTC cleared. A thorough test-drive confirmed that the fault had been corrected and the shop learned that the proper viscosity oil is important to use in all vehicles.
 
SUMMARY:  
Complaint The check engine light was on after an oil change.
Cause The incorrect viscosity oil was used.
Correction The oil was replaced with the specified viscosity and the DTC was cleared.
 
The Case of the Wrong Oil Viscosity
A Dodge Durango 5.7 liter Hemi with a multiple displacement system (MDS) had the oil changed at a shop. SAE 10W-30 was used as this was the “standard” bulk oil in the shop. After the oil change, the vehicle was returned to the customer. Within a few minutes, however, the “check engine” light came on. The technician checked for diagnostic trouble codes (DTCs) and found a P0521 DTC stored. The technician checked service information and discovered that the code could be set if the incorrect viscosity engine oil had been used. The description of the P0521 read: “Oil pressure not reaching specified at 1250 RPM.” The technician changed the oil and used the specified SAE 5W-20, then cleared the DTC. A test drive confirmed that the change to the correct viscosity oil solved the problem.
 
SUMMARY:  
Complaint Customer stated that the “check engine” came on after an oil change.
Cause The incorrect viscosity of oil was used.
Correction The specified viscosity oil (SAE 5W-20) was used and the code cleared.
 
The Cavalier Convertible Story
The owner of a Cavalier convertible stated to a service technician that the “check engine” (MIL) was on. The technician found a diagnostic trouble code (DTC) for a MAP sensor. The technician removed the hose at the MAP sensor and discovered that gasoline had accumulated in the sensor and dripped out of the hose as it was being removed. The technician replaced the MAP sensor and test drove the vehicle to confirm the repair. Almost at once the check engine light came on with the same MAP sensor code. After several hours of troubleshooting without success in determining the cause, the technician decided to start over again. Almost at once, the technician discovered that no vacuum was getting to the MAP sensor where a vacuum gauge was connected with a T-fitting in the vacuum line to the MAP sensor. The vacuum port in the base of the throttle body was clogged with carbon. After a thorough cleaning, and clearing the DTC, the Cavalier again performed properly and the check engine light did not come on again. The technician had assumed that if gasoline was able to reach the sensor through the vacuum hose, surely vacuum could reach the sensor. The technician learned to stop assuming when diagnosing a vehicle and concentrate more on testing the simple things first.
 
SUMMARY:  
Complaint Customer stated that the “Check Engine” warning light was on.
Cause The vacuum post to the MAP sensor was found to be clogged.
Correction Cleaning the vacuum port at the throttle body restored proper operation of the MAP sensor.
 
The Chevrolet Pickup Truck Story
The owner of a 1996 Chevrolet pickup truck complained that the engine ran terribly. It would hesitate and surge, yet there were no diagnostic trouble codes (DTCs). After hours of troubleshooting, the technician discovered while talking to the owner that the problem started after the transmission had been repaired, yet the transmission shop said that it was an engine problem and not related to the transmission. A thorough visual inspection revealed that the front and rear oxygen sensor connectors had been switched. The computer was trying to compensate for an air–fuel mixture condition that did not exist. Reversing the O2S connectors restored proper operation
 
SUMMARY:
Complaint Customer stated that the truck ran terribly after the transmission was replaced.
Cause A visual inspection was used to determine a that the the upstream and downstream oxygen sensor connector had been switched.
Correction Connecting the oxygen senors to the correct harness connector restored proper engine operation.
 
The Collapsed Radiator Hose Story
An automotive student asked the automotive instructor what brand of radiator hose is the best. Not knowing exactly what to say, the instructor asked if there was a problem with the brand hose used. The student had tried three brands and all of them collapsed when the engine cooled. The instructor then explained that the vehicle needed a new pressure cap and not a new upper radiator hose. The student thought that because the lower hose did not collapse that the problem had to be a fault with the hose. The instructor then explained that the lower radiator hose has a spring inside to keep the lower hose from collapsing due to the lower pressure created at the inlet to the water pump. The radiator cap was replaced and the upper radiator hose did not collapse when the engine cooled.
 
SUMMARY:  
Complaint Vehicle owner stated the upper radiator hose would collapse when the engine cools.
Cause The upper radiator collapsed due to a fault with the radiator pressure cap.
Correction A new radiator cap solved the problem.
 
The Dirty MAF Sensor Story
The owner of a Buick Park Avenue equipped with a 3,800 V-6 engine complained that the engine would hesitate during acceleration, showed lack of power, and seemed to surge or miss at times. A visual inspection found everything to be like new, including a new air filter. There were no stored diagnostic trouble codes (DTCs). A look at the scan data showed airflow to be within the recommended 3 to 7 grams per second. A check of the frequency output showed the problem.
Idle frequency ∙ 2.177 kHz (2,177 Hz)
Normal frequency at idle speed should be 2.37 to 2.52 kHz. Cleaning the hot wire of the MAF sensor restored proper operation. The sensor wire was covered with what looked like fine fibers, possibly from the replacement air filter.
 
SUMMARY:  
Complaint Customer stated that the engine hesitated when accelerating.
Cause Tests confirmed that the MAF sensor was was operating correctly but the frequency output at idle was not within the normal range.
Correction Cleaning the MAF sensor restored proper operation of the sensor and the engine now accelerates normally.
 
The High Idle Toyota
The owner of a Toyota Camry complained that the engine would idle at over 1200 RPM compared with a normal 600 to 700 RPM. The vehicle would also not accelerate. Using a scan tool, a check for diagnostic trouble codes showed one code: P2101—“TAC motor circuit low.” Checking service information led to the inspection of the electronic throttle control throttle body assembly. With the ignition key out of the ignition and the inlet air duct off the throttle body, the technician used a screwdriver to see if the throttle plate worked. Normal operation—The throttle plate should move and then spring back quickly to the default position. Abnormal operation—If the throttle plate stays where it is moved or does not return to the default position, there is a fault with the throttle body assembly. The technician replaced the throttle body assembly with an updated version and proper engine operation was restored. The technician disassembled the old throttle body and found it was corroded inside due to moisture entering the unit through the vent hose.
 
SUMMARY:
Complaint Customer stated that the engine would idle at over 2,000 RPM.
Cause A stored P2101 DTC was stored indicating a fault with the throttle body assembly.
Correction The throttle body was replaced with an improved version that placed the vent tube in a different position to help avoid water getting into the assembly.
 
The Missing Ford pickup truck
A Ford pickup truck was being analyzed for poor engine operation. The engine ran perfectly during the following conditions:
1. With the engine cold or operating in open loop
2. With the engine at idle
3. With the engine operating at or near wide-open throttle
After hours of troubleshooting, the cause was found to be a poor ground connection for the oxygen sensor. The poor ground caused the oxygen sensor voltage level to be too high, indicating to the computer that the mixture was too rich. The computer then subtracted fuel, which caused the engine to miss and run rough as the result of the now-too-lean air–fuel mixture.
 
SUMMARY:
Complaint Customer stated that the engine ran poorly except when cold or at wide open throttle and at idle speed.
Cause Tests discovered a poor ground for the oxygen sensor which cause the signal to be higher than it should.
Correction Cleaning the electrical terminals at the ground connection on the engine block restored proper oxygen sensor operation.
 
The Mysterious Engine Vibration
A Buick 3.8 liter V-6 engine vibrated the whole car after a new short block had been installed. The technician who had installed the replacement engine did all of the following:
1. Checked the spark plugs
2. Checked the spark plug wires
3. Disconnected the torque converter from the flex plate (drive plate) to eliminate the possibility of a torque converter or automatic transmission pump problem
4. Removed all accessory drive belts one at a time Yet the vibration still existed. Another technician checked the engine mounts and found that the left (driver’s side) engine mount was out of location, ripped, and cocked. The transmission mount was also defective. After the technician replaced both mounts and made certain that all mounts were properly set, the vibration was eliminated.
 
SUMMARY:  
Complaint Vehicle vibrated after a replacement engine block was installed.
Cause Defective engine and transmission mounts.
Correction Both mounts were replaced which corrected the vibration.
 
The Noisy Camshaft
The owner of an overhead cam 4-cylinder engine complained of a noisy engine. After taking the vehicle to several technicians and getting high estimates to replace the camshaft and followers, the owner tried to find a less expensive solution. Finally, another technician replaced the serpentine drive belt on the front of the engine and “cured” the “camshaft” noise for a fraction of the previous estimates.
Many engines have been disassembled and/or overhauled because of a noise that was later determined to be from one of the following:
• Loose or defective accessory drive belt(s)
• Loose torque converter-to-flex plate (drive plate) bolts (nuts)
• Defective mechanical fuel pump (if equipped)
 
SUMMARY:  
Complaint Vehicle owner complained about an noisy engine.
Cause A defective accessory drive belt was found to be the cause of the noise.
Correction The accessory drive belt was replaced.
 
The Oil Burning Chevrolet Astro Van
An automotive instructor was driving a Chevrolet Astro van to Fairbanks, Alaska, in January. It was pretty cold out, somewhere around -32°F (-36°C). As he pulled into Fairbanks and stopped at a traffic light, he smelled burning oil. When he stopped at the hotel he still smelled burning oil. He looked under the van and discovered a large pool of oil. After checking the oil and finding very little left, he called a local shop and was told to bring it in. The technician looked over the situation and said, “You need to put some cardboard across the grill to stop the PCV valve from freezing up.” Apparently the PCV valve froze, which then caused the normal blowby gases to force several quarts out the dipstick tube. After he installed the cardboard, he did not have any further problems.
Caution: Do not cover the radiator when driving unless under severe cold conditions and carefully watch the coolant temperature to avoid overheating the engine.
SUMMARY:  
Complaint Vehicle owner experienced oil burning when extremely cold outside.
Cause The PCV valve was frozen causing pressure to build up in the crankcase.
Correction Placing some cardboard in front of the radiator prevented the valve from freezing and allowed the crankcase ventilations system to function normally.
 
The Oxygen Sensor Is Lying to You
A technician was trying to solve a driveability problem with an older V-6 passenger car. The car idled roughly, hesitated, and accelerated poorly. A thorough visual inspection did not indicate any possible problems and there were no diagnostic trouble codes stored. A check was made on the oxygen sensor activity using a DMM. The voltage stayed above 600 mV most of the time. If a large vacuum hose was removed, the oxygen sensor voltage would temporarily drop to below 450 mV and then return to a reading of over 600 mV. Remember:
• High O2S readings = rich exhaust (low O2 content in the exhaust)
• Low O2S readings = lean exhaust (high O2 content in the exhaust)
As part of a thorough visual inspection, the technician removed and inspected the spark plugs. All the spark plugs were white, indicating a lean mixture, not the rich mixture that the oxygen sensor was indicating. The high O2S reading signaled the computer to reduce the amount of fuel, resulting in an excessively lean operation. After replacing the oxygen sensor, the engine ran great. But what killed the oxygen sensor? The technician finally learned from the owner that the head gasket had been replaced over a year ago. The phosphate and silicate additives in the antifreeze coolant had coated the oxygen sensor.
 
SUMMARY:
Complaint Customer stated that the engine idled roughly and hesitated while accelerating.
Cause Tests indicated that the oxygen sensor was skewed high.
Correction Replacing the oxygen sensor restored proper engine operation.
 
The Radio Caused No-Start Story
A 2012 GMC pickup truck did not start. A technician checked with a subscription-based helpline service and discovered that a fault with the Class 2 data circuit could have prevented the engine from starting. The advisor suggested that a module be disconnected one at a time to see if one of them was taking the data line to ground. The two most common components on the Class 2 serial data line that have been known to cause a lack of communication and become shorted-to-ground are the radio and electronic brake control module (EBCM). The first one the technician disconnected was the radio. The engine started and ran. Apparently the Class 2 serial data line was shorted-to-ground inside the radio, which took the entire BUS down. When BUS communication is lost, the PCM is not able to energize the fuel pump, ignition, or fuel injectors so the engine would not start. The radio was replaced to solve the no-start condition.
 
SUMMARY:
Complaint Customer stated that the truck would not start.
Cause The Class 2 serial data line was shorted to ground inside the radio.
Correction The radio was replaced which restored proper operation of the Class 2 serial data communications.
 
The Start/Stall/Start/Stall Problem
A Chevrolet 4-cylinder engine would stall every time it was started. The engine cranked normally and the engine started quickly. It would just stall once it had run for about 1 second. After hours of troubleshooting, it was discovered that if the “gages” fuse was removed, the engine would start and run normally. Because the alternator was powered by the “gages” fuse, the charging voltage was checked and found to be over 16 volts just before the engine stalled. Replacing the alternator fixed the problem. The computer shut down to prevent damage when the voltage exceeded 16 volts.
 
SUMMARY:  
Complaint Engine would stall every time it started.
Cause The alternator was over charging causing the PCM to shut off the engine to protect itself against the higherthan- normal voltage.
Correction Replacing the alternator corrected the engine stall after start concern.
 
The Two Minute Alternator Repair
A Chevrolet pickup truck was brought to a dealer for routine service. The owner stated that the battery required a jump start after a weekend of sitting. The technician tested the battery and charging system voltage using a small handheld digital multimeter. The battery voltage was 12.4 volts (about 75% charged), but the charging voltage was also 12.4 volts at 2000 RPM. Because normal charging voltage should be 13.5 to 15 volts, it was obvious that the charging system was not operating correctly. The technician checked the dash and found that the “charge” light was not on. Before removing the alternator for service, the technician checked the wiring connection on the alternator. When the lead regulator connector was removed, the connector was discovered to be rusty. After the contacts were cleaned, the charging system was restored to normal operation. The technician had learned that the simple things should always be checked first before tearing into a big (or expensive) repair.
 
SUMMARY:  
Complaint Battery was dead after sitting over the weekend.
Cause The alternator was not charging due to a poor electrical connection at the alternator.
Correction The electrical connector was cleaned and the charging system was restored to normal operation.
 
The Weird Running Chevrolet Truck
An older Chevrolet pickup truck equipped with a V-8 engine was towed into a shop because it would not start. A quick check of the ignition system showed that the pickup coil had a broken wire below it and the ignition control module. The distributor was removed from the engine and the distributor shaft was removed, cleaned, and a replacement pickup coil was installed. The engine started but ran rough and hesitated when the accelerator pedal was depressed. After an hour of troubleshooting, a careful inspection of the new pickup coil showed that the time core had six instead of eight points, meaning that the new pickup coil was meant for a V-6 instead of a V-8 engine. Replacing the pickup coil again solved the problem.
 
SUMMARY:  
Complaint Customer stated that the truck would not start.
Cause A visual inspection was used to determine a that a pickup coil wire was broken and was replaced but with the wrong part that was in the correct box.
Correction Replacing the pickup coil with the right part fixed the truck.
 
The Whistling Engine
An older vehicle was being diagnosed for a whistling sound whenever the engine was running, especially at idle. It was finally discovered that the breather in the valve cover was plugged and caused high vacuum in the crankcase. The engine was sucking air from what was likely the rear main seal lip, making the “whistle” noise. After replacing the breather and PCV, the noise stopped.
 
SUMMARY:  
Complaint Vehicle owner complained that the engine would make a whistling noise.
Cause The crankcase breather was clogged.
Correction The breather and the PCV valve were both replaced which stopped the whistling noise when the engine was running.
 
There Is No Substitute for a Thorough Visual Inspection
An intermittent “check engine” light and a randommisfire diagnostic trouble code (DTC) P0300 was being diagnosed. A scan tool did not provide any help because all systems seemed to be functioning normally. Finally, the technician removed the engine cover and discovered a mouse nest.
 
SUMMARY:
Complaint Customer stated that the “Check Engine” light was on.
Cause A stored P0300 DTC was stored indicating a random misfire had been detected caused by an animal that had partially eaten some fuel injector wires.
Correction The mouse nest was removed and the wiring was repaired.
 
Valve Springs Can Vary
A technician was building a small block Chevrolet V-8 and found that many of the valve springs did not have the same tension. Using a valve spring tester, the technician visited a local parts store and measured all of the valve springs that the store had in stock. The technician selected and purchased the 16 valve springs that were within specification and within a very narrow range of tension. Although having all valve springs equal may or may not affect engine operation, the technician was pleased that all of the valve springs were equal.
 
SUMMARY:  
Complaint A technician discovered that valve springs did not all have the same tension.
Cause Due to manufacturing tolerances, valve springs can vary in tension.
Correction The technician tested all available springs and selected those that were the most equal in tension.
 

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Engine Runs Rough after the Oil Pan Is Resealed
The customer, with a 2002 Ford truck equipped with a Power Stroke engine, complained that the engine was running rough. The concern was verified and a review of the service history revealed a recent repair of an engine oil leak. After a thorough inspection revealed no other concerns, the oil and filter were changed to correct the problem. When the oil leak repair was completed, an antifoaming additive should have been added to the engine oil, or the next oil change interval should have been shortened. Many RT V sealants release a chemical during the curing process that depletes the effectiveness of the antifoam additive. The lack of the antifoam additive caused low pressure in the high-pressure oil system which resulted in the rough running that the customer complained about.
 
SUMMARY:
Complaint The customer complained of a rough running concern after an engine oil leak was repaired.
Cause The engine oil antifoaming additive was depleted because of the chemicals given off by the RT V sealant during the curing process.
Correction The engine oil and filter were changed and the problem was resolved.
 
Multiple Injector Driver Module Replacements
A 2004 Ford truck with a Power Stroke was in the shop for a rough running concern. An inspection revealed that the engine was misfiring on four cylinders. It was determined that the injector driver module (IDM) had failed. A replacement injector driver module (IDM) was installed and the misfire was still present. A further inspection revealed a single injector was shorted to ground. The shorted injector and the injector module were replaced, correcting the misfire condition. The failure of the module was caused by the shorted injector. The shorted injector shared a common low-side driver with three other injectors, causing the multiple cylinder misfire.
 
SUMMARY:
Complaint The truck had a rough running condition.
Cause A shorted injector was causing a misfire condition on four cylinders, and had damaged the injector driver module.
Correction The shorted injector and the damaged injector driver module (IDM) were both replaced and the misfire condition was corrected.
 
The Case of the Duramax EGR Low Flow
The owner of a 2006 GMC truck with a 6.6L Duramax Diesel engine with 35,578 miles was in the shop with a complaint of a malfunction indicator lamp (MIL) illuminated and reported no drivability concerns. A diagnosis with the scan tool found a diagnostic trouble code (DTC) for low EGR flow (P0401). A functional test with the scan tool verified the electrical operation of the EGR valve; however, the valve failed the flow test. Upon disassembly, the passageways in the EGR valve and EGR cooler were found to be nearly closed off due to heavy carbon buildup. The cause of the buildup was determined to be excessive idle time and low engine temperatures. The EGR valve and the EGR cooler were both replaced and the intake passages were cleaned.
 
SUMMARY:
Complaint The owner of the diesel pickup truck complained that the “check engine” light was on with no apparent problems with the operation of the engine.
Cause A stored code P0401 (low EGR flow) was retrieved, indicating that the EGR passages were likely restricted.
Correction The EGR and EGR cooler were both replaced to correct the low EGR flow concern.
 
The Case of Erratic Electrical Symptoms
The owner of a 2010 Dodge Truck with a 6.7-Liter Cummins engine complained of a noticeable change in the level of the interior or exterior lighting, as well as the speed of the blower motor. The owner stated that this situation occurred just after starting the truck. The service technician was able to verify the customer concern and monitored the battery voltage using a scan tool to confirm what the technician thought was happening. The intake heaters on the Cummins 6.7 draw so much current that the battery voltage is reduced, causing the diming of the interior lights and the blower motor to turn slower than normal. The intake manifold heaters may continue to run for several minutes after the vehicle has started. No repairs were made and the customer was informed as to why this situation was occurring.
 
SUMMARY:
Complaint Customer complained that the interior lights were dimmer than normal shortly after starting the engine.
Cause The battery voltage was reduced by the high amperage draw of the intake heaters.
Correction No repairs were needed and the customer was informed that this was a normal condition on this diesel pickup.
 
The Case of the Failed EGR system
A 2013 Ford F250 with a 6.7 liter Power Stroke engine was in the shop with a malfunction indicator lamp (MIL) illuminated. The customer noticed the malfunction indicator lamp (check engine) was illuminated, but the vehicle exhibited no drivability concerns. A P0401 (low EGR flow) code was recorded and the EGR cooler was found to be restricted. A check of the truck’s hour meter found a high percentage of idle time. A sample of the vehicles fuel indicated a low cetane level. The EGR cooler was replaced and the customer was instructed to shut off the vehicle instead of letting it idle excessively. It was also suggested that the customer treat the fuel with an additive to improve the cetane level.
 
SUMMARY:
Complaint The owner of Ford F250 equipped with a 6.7 liter Power Stroke diesel engine complained that the check engine light was on, but the truck seemed to be running fine.
Cause A P0401 (Low EGR Flow) code was recorded and the EGR cooler was found to be restricted.
Correction The EGR cooler was replaced and the customer was instructed to shut off the vehicle instead of letting it idle excessively.
 
The Case of the High-Pressure Fuel System Components Failure
A 2012 Ford truck equipped with a 6.7 liter Power Stroke diesel engine was recently in the shop with a complaint of being hard to start and running rough. The malfunction indicator lamp (MIL) was illuminated. A code scan of the PCM found a P1292 (injector shorted to voltage or ground). A test of the high-pressure fuel system return volume to the tank revealed an amount above specifications. It was determined that the high-return volume was a result of internal wear in the numerous injectors. Further investigation revealed that the wear was due to fuel contamination by diesel exhaust fluid (DEF). The presence of DEF in the injectors was also responsible for the P1292 code. DEF crystals were found in the primary fuel filter. To correct the condition, the fuel system was cleaned, the fuel filters were replaced, and all eight injectors were replaced per the Ford Technical Service Bulletin # 11-10-10.
 
SUMMARY:
Complaint The customer complained the vehicle was hard to start, the engine ran rough, and the MIL was illuminated.
Cause The failure was a result of diesel exhaust fluid (DEF) in the fuel system.
Correction Per the Ford TSB #11-10-10, the fuel system was cleaned, the fuel filters were replaced, and all eight injectors were replaced.
 
The Case of the Limited Engine Speed
A customer was concerned that the 6.6 Duramax engine ran great, but would not rev over 2,200 RPM. The service technician checked and did not find any stored diagnostic trouble codes (DTC s) or any technical service bulletins (TSBs) that were related to this fault. A quick check with other technicians revealed that if the power take-off (PTO) button was in the “on” position, this would cause the engine to not rev higher than 2,200 RPM. The PTO button was found to be in the “on” position and the PTO speed set to 2,200 RPM. After turning the PTO button to “off,” the engine operated normally.
 
SUMMARY:
Complaint Customer stated that the diesel engine would not rev faster than 2,200 RPM.
Cause The power take-off (PTO) button was in the “on” position, which limited the maximum engine speed to 2,200 RPM.
Correction The PTO button, located below the climate controls in the center of the vehicle instrument panel, was turned to “off” and this solved the customer concern.
 
The Case of the Loose Transfer Tubes
The owner of a 2010 Dodge Ram equipped with a 6.7 liter Cummins diesel engine is in the shop complaining of a rough running engine. A review of the vehicle’s service history revealed the vehicle had recently had the injectors and connecting tubes replaced for a similar complaint. An inspection of the work previously performed found the retaining nuts for the #5 and #6 connecting tubes below the manufacturers torque specification. Re-torqueing the retaining nuts to specifications eliminated the rough running condition. The system did not have any internal leaks, however, the under-torqued retaining nuts allowed air to be drawn into the high-pressure fuel system, creating the rough running condition.
 
SUMMARY:
Complaint The customer complained of a rough running engine.
Cause The #5 and #6 transfer tube retaining nuts were under-torqued.
Correction Re-torqued the transfer tube retaining nuts to specifications.
 
The Case of the Multiple Injector Washers
A 2009 Dodge Ram with a 5.9 liter Cummins engine was in the shop with a complaint of hard to start and a lack of power on acceleration. The vehicle had all six injectors replaced recently at another shop. A test of the fuel return volume indicated an abnormally high return volume. After removing all six of the previously installed injectors, the number five injector was found to have two sealing washers at the tip. One of the washers was new and the other washer was original to the engine and was not removed when the injector was replaced. The additional washer caused damage to the new injector and the cylinder head. Both the cylinder head and the new injector had to be replaced to solve the customer concern.
 
SUMMARY:
Complaint The customer complained the vehicle was hard to start and lacked power on acceleration.
Cause The number five replacement injector was installed with two sealing washers (the original and the replacement), causing damage to the cylinder head and the injector.
Correction The cylinder head and the injector were both replaced.
 
The Case of the Noisy 7.3-Liter Power Stroke Starter
The owner of a 2002 Ford F-Super Duty equipped with the 7.3-liter turbo diesel engine complained about a buzzing/screeching starter noise during some engine start attempts. The customer thought that the engine needed a new starter. The service technician was aware that the diesel starter mounting bolts can loosen over time, so they were checked first. Both bolts on the two-bolt starter were found to be extremely loose, allowing the starter to jump around with intermittent engagement of the starter drive. The original factory specification for the 10 mm * 1.5 bolts calls for 16-20 ft.-lbs. However, replacement starter instructions specified a torque specification of 40-57 ft.-lbs. The technician decided to tighten both bolts to 50 ft.-lbs., about in the middle of the latest specifications. After tightening the starter bolts, the noisy starter problem was solved. The truck owner was very happy because a new starter was not needed.
 
SUMMARY:
Complaint The owner complained of a noisy starter.
Cause Loose starter attachment bolts were found.
Correction The starter bolts were tightened to specifications found in replacement starter instructions.
 
The Case of the Stuck Open EGR Valve
The owner of a 2011 Ford Power Stroke stated that while driving down the highway, the engine lost power. The engine was still running, but it had no power and would blow black smoke from the exhaust when accelerating. The technician retrieved a P1355 DTC (exhaust gas recirculation (EGR) position sensor minimum/maximum stop performance). An inspection of the EGR valve showed that it was stuck open by a large carbon particle that looked like a small rock. The most likely cause of this type of failure is due to a small coolant leak in the EGR cooler, which causes carbon particles to loosen and break off, causing the EGR valve to become clogged. This fault required that the EGR cooler be replaced and the EGR valve cleaned. After the repair, the truck ran normally.
 
SUMMARY:
Complaint Vehicle owner complained that the engine lost power while driving.
Cause A stuck open EGR valve caused by carbon particles from a defective EGR cooler.
Correction The EGR cooler was replaced and the EGR valve was cleaned, which restored proper engine operation.
 
The Case of the Tuner Program Gone Bad
The owner of a two-year-old Duramax complained to the dealer service department that the engine was not running smoothly and had a check engine light on. A check of the diagnostic trouble codes indicated a stored P0300 (random misfire code) DTC . The service technician verified that the engine had a noticeable misfire, plus noticed some engine noise. When one of the valve covers was removed to check for possible valve train-related issues, several bent pushrods were discovered. Because the engine was still under the factory warranty, the factory service rep was called in for help. The district rep discovered the following:
1. The PCM had been reflashed 5 times, yet the factory program was currently installed.
2. The engine had been operated up to 5,500 RPM, which is much higher than the factory programming allowed. Based on these findings, the warranty was canceled on the engine. The customer was notified that while a hand-held tuner can be used to recalibrate the PCM to increase engine power, it does so by “taking the emissions out of compliance” and can often cause engine damage as in this case. The owner decided to have the engine repaired and left the programming of the PCM the same as when it left the factory.
 
SUMMARY:
Complaint The owner complained of a rough running engine and the check engine light was on.
Cause The engine had been operated at a speed that was higher than it was designed to operate, which caused several pushrods to be bent.
Correction The bent pushrods were replaced, at the customer’s expense, which corrected the rough running engine concern.
 

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