AGCO Automotive Vehicle Questions Page

AGCO Automotive Vehicle Questions
Electrical Systems and Warning Lights
QUESTIONS
  1. After doing some under-dash work, my SIR light is on. How can I reset the light?
  2. After having the water pump on my car replaced, the check engine light has come on. What is the best way to handle this with the shop?
  3. An oxygen sensor caused the check engine light to come on in my vehicle. What is the purpose of an oxygen sensor?
  4. Can an alternator bearing be replaced?
  5. Can corroded battery cables cause an engine to run rough?
  6. Can water short out an alternator?
  7. Can you help? I have an old Suburban and the left turn signal flashes very fast, while the right flashes at normal speed?
  8. Codes P0174, P0171 and P0300 were set on my GMC Sierra. I had the intake gaskets replaced and 18 months later I have the same codes again. Why would this keep happening?
  9. Does being low on oil make a check engine light come on?
  10. Does my replacement battery need to be the same size as the original?
  11. Does the check engine light come on for automatic transmission problems?
  12. Does the check Engine light come on when my vehicle needs routine maintenance?
  13. Every so often, when I try to start my Toyota, I just get a click and it does not crank over. After a few tries it cranks fine. I have replace the battery and checked the cables.
  14. How can I be sure I get the correct replacement vehicle battery?
  15. How can I check my fuel gauge to see if the problem is the sender or the gauge?
  16. How can I tell how many amp alternator I have with out taking it off?
  17. How does the check fuel cap light work?
  18. How does the warranty on a battery work?
  19. How many amps should my starter draw when cranking?
  20. How much of a drain is the alternator on the engine?
  21. I am taking a long trip, can an alternator be tested to determine if it might fail?
  22. I had my timing belt replaced and after leaving the shop my ABS light came on after 10 miles. I returned to the shop and was told the ABS module had failed. I am very suspicious, what do you think?
  23. I had the rack and pinion replaced in my vehicle and when I picked it up the air bag light was on. The shop says it is not related to the work they did. Could this be a coincidence?
  24. I have a light that says SIR, what does it mean?
  25. I have an odor, almost like rotten eggs coming from under the hood of my vehicle.
  26. I have an older Chevy pick up that runs fine, but my air bag light stays on. What does this mean?
  27. I have code P0305, P0307 and P0132 on my Chevrolet pickup and it idles roughly. I have changed the O2 sensors, spark plugs, wires, distributor, cap and rotor. The same codes are still present. A friend says it might be the head gasket.
  28. I have no brake lights and the shop is telling me it is the turn signal switch. How can the turn signal switch keep the brake lights from working?
  29. I have one turn signal bulb that keeps going out. I replace it and about six months later it goes out again.
  30. I have seen code readers advertised in several magazines. Can I save money by buying one of these and fixing my own vehicles?
  31. I have several weird electrical problems with my vehicle. Where is the best place to start looking?
  32. I just bought a used Ford and noticed the fuel gauge wasn't working. What could be the problem?
  33. I put a locking gas cap on my car and now the check engine light comes on?
  34. I was involved in a rear collision and the next day my check engine light came on. The code indicates EGR failure, could this be related to the accident?
  35. In the last few days a red light that says BRAKE comes on, remains for a several seconds and then goes back off. It seems to be related to turning a corner and accelerating.
  36. Is hot weather or cold weather worse on a car battery?
  37. Is it possible for a fuse to look okay and still be blown?
  38. Is there a way to disable the check engine light on my Suburban?
  39. My ABS brake light is on but there are no symptoms.
  40. My battery cables are corroded, should I replace the ends with bolt on terminals?
  41. My battery terminal keep corroding and I was told my battery is leaking. My car starts fine, do I need to replace the battery?
  42. My brake lights are not working. How can I test for the brake light switch?
  43. My check engine light came on about a year ago. The car still runs well but the light is still on. Is this anything to be concerned about?
  44. My check engine light came on and a friend told me I should disconnect the battery and see if it goes off? Would you recommend that I do this?
  45. My check engine light came on and after repair the invoice listed code P0304. Does this code have a specific meaning?
  46. My check engine light came on and stayed on all day. The next day it did not come on and has not come on in two days. Is this still a problem?
  47. My check engine light is on and I am told it is the EGR valve. Can I still drive the vehicle with the EGR valve not working?
  48. My check engine light was on so I had a friend clear the codes. When I went to get an inspection sticker I was rejected because the readiness test were incomplete.
  49. My check engine light was on, I had it repaired then it came on again. I returned to the shop, had more repair done and now it is on again. This is the third time in a year, it seems the shop is not doing something right.
  50. My driver’s side low beam headlight keeps going out. I have changed it three since I bought the car in 60,000 miles.
  51. My engine would not crank when I turn the key. I replaced the starter relay, it tried to crank, but the relay immediately burned out. What would cause this?
  52. My Maxima's starter has begun to occasionally miss engaging the ring gear on start-up and makes a loud ZING! Which rebuilt starter brand is the best to use?
  53. My truck quit running two weeks ago. A friend checked it and told me there was no fuel pressure. I replaced the fuel pump and it ran for a couple of hours and then died again. Do you think this pump is defective?
  54. My vehicle came equipped with ten-ply tires. The tire pressure monitoring system was set for 50 PSI. I would like to reduce the air pressure to improve ride. Can I do this without making the warning light come on?
  55. My vehicle failed the State emissions inspection and I was told it was because my cigarette lighter did not work. How can that be?
  56. My vehicle was recently wrecked in the front but the air bag did not deploy. Is this a defect?
  57. Only my top brake light is working and not the two main brake lights. The turn signals work and the hazard flashers work as well. All fuses are okay.
  58. Recently I had to have head gaskets replaced on my vehicle. The shop said the car had been over heated, but the warning light never came on. Is this possible?
  59. Recently my vehicle air conditioner was repaired. Shortly after picking the vehicle up, the check engine light came on. Could this be a coincidence?
  60. Several alternators have been replaced on my vehicle. Is this just poor quality parts?
  61. Some part stores offer to read codes for free when a check engine light comes on. What is the advantage to having a professional diagnosis?
  62. The ABS light came on and the wheel speed sensor was replaced. Less than a year later the light came back and the sensor was again replaced. Two weeks later the light is back on. Why does the sensor keep failing?
  63. The air conditioner blower in my vehicle quit working. I replaced the blower resistor and it worked for a while and quit. Could the switch be bad and how can I check it?
  64. The anti lock brake light is on in my vehicle, but no codes show with a code reader.
  65. The battery in my vehicle goes dead over night. If I disconnect the cable from the battery and reconnect in the morning it is good. What could cause this?
  66. The brake lights on my Honda Accord are staying on, even though the pedal is not being pressed. What would cause a problem like this?
  67. The center brake light on my vehicle lights but the regular brake lights do not. The fuse, bulb, sockets and brake switch all test good. What could be the problem?
  68. The check engine light came on and a part store told me it was the gas cap. I replaced the cap and the light is still on. How can this be?
  69. The check engine light is on in my Yukon and I was told the intake manifold is leaking. I can see nothing leaking under or around the vehicle.
  70. The Check Engine light on my Ford is on. I took the vehicle to a part store and was told I needed an EGR valve. I bought the valve, replaced it, but the light still comes on.
  71. The check engine light was on in my car. A parts store cleared the codes but my car still failed inspection.
  72. The company I work for rents a van from a large rental firm. The check engine light is always on and when we bring it to the rental companies attention, they simply clear the code. The next day the light is back. Should I be concerned?
  73. The fuel gauge on my Impala shows 1/4 tank but the driver information center reads low?
  74. The low coolant light came on in my vehicle and the coolant reservoir was empty. I filled the reservoir but the light is still on. Do you think the level sensor is the cause?
  75. The oil pressure gauge in my Chevy Suburban moves from zero to maximum when I start the truck. Could this be the gauge?
  76. The oil pressure gauge on my GMC Sierra is stuck all the way on high. Do I have to take this to a GM dealership?
  77. The oil pressure light came on in my car while I was driving. I stopped checked the oil and it was full. When I started again the light was out but later came on again, does this sound like a major engine problem.
  78. The speedometer of my Chevy Suburban often sticks and reads improperly. I was told this was under recall, but the dealership told me it had expired. What is the term of the recall?
  79. The terminals of my battery keep corroding. I clean them and within a few weeks it has occurred again. Is there a way to prevent this?
  80. This morning when I went to start my car there was a click, click noise and the engine would not crank over. Do you think this is just the battery or should I have the electrical system checked?
  81. What are the symptoms of a bad alternator?
  82. What do OBDII codes actually mean?
  83. What does a flashing over-drive light indicate?
  84. What does the check suspension message on my Lincoln indicate?
  85. What does the dash gauge marked RPM do?
  86. What does the light labeled “Check Engine” indicate?
  87. What does the term OBDII mean in reference to my vehicle?
  88. What is a starter solenoid and how does it work?
  89. What is an automotive O2 sensor used for?
  90. What is needed to test an automotive relay?
  91. What is the average life of an automobile battery?
  92. What is the difference in a deep cycle and regular car battery?
  93. What is the difference in a deep cycle battery and a regular car battery?
  94. What is the purpose of an alternator?
  95. When I turn my ignition switch to start I hear a loud click, but nothing else. Sometimes it will do this several times and then start. This is a General Motors vehicle.
  96. When should I replace my vehicle battery?
  97. Why is the starter on my new car much smaller than the one on my older car?
  98. Why would my vehicle battery overheat?
  99. Without test equipment, is there a way to determine the cause of a misfire on an old carburetor type engine?
  100. Would a bad brake caliper cause the ABS and Traction control light to come on?
  101. Would a deep cycle battery last longer in a vehicle I do not drive often?
ANSWERS
  1. After doing some under-dash work, my SIR light is on. How can I reset the light?

    The supplemental inflatable restraint or SIR system is self-testing and resetting. When the light is on, there is an active fault in the system. Check all wiring connections, in the air bag system. These are normally color coded yellow for identification. When the problem, causing the fault, is corrected, cycle the ignition switch. The light will go out, after a short self-test.
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  2. After having the water pump on my car replaced, the check engine light has come on. What is the best way to handle this with the shop?

    While such things should not happen, sometimes they do. Best is politely to inform the shop that there is a problem and ask them to check it for you. Most shops will be happy to correct any problem, caused by their work.

    It is also possible this is a coincidental occurrence and not related to the work they did. If this is what the shop finds, and you do not agree with their explanation, a second opinion would be appropriate. In the Detailed-Topics section, there is an article entitled When Things Go Wrong that has a lot more information on this topic.


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  3. An oxygen sensor caused the check engine light to come on in my vehicle. What is the purpose of an oxygen sensor?

    Oxygen sensors come in several types and serve different functions. Vehicles may have as few as one, or two, three, four or more. The basic function is to tell the power control module or PCM, how complete combustion has been. The PCM uses this information to control the fuel injectors and thus how much fuel is mixed with the air entering the engine.

    When too much fuel is added, economy will suffer and components can be damaged. If there is not enough fuel, in relation to the air, running problems and damage to components can occur. Improper mixture can also result in damage to the catalytic converter(s) which can be extremely expensive.

    Oxygen sensors are also used to monitor the function of the catalytic converter and test its efficiency, on post OBDII vehicles.

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  4. Can an alternator bearing be replaced?

    In most cases, it is possible to replace just the bearing(s) if they are available. This is sometimes done on very expensive or hard to find alternators. In most other cases, alternators are replaced with a rebuilt unit, because of costs. It requires significantly more time to replace the bearing than to install another unit. Time is money and it may be less expensive to replace the alternator rather than repair it. Other considerations are, when the bearing fails other components, such as brushes, diodes and even wiring, may not be far behind.
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  5. Can corroded battery cables cause an engine to run rough?

    Many things can cause an engine to run rough and while battery cables are not normally associated with this symptom, it is possible. Idle is a learned function on modern vehicles. The power control module (PCM) uses several inputs to determine idle. It also retains data, which allows for smooth idle under various conditions. Corroded cables can reduce system voltage and cause loss of this memory. When that happens, idle can be rough as well as several other problems.

    For even more information on batteries and cables, see our Detailed Topics article, Replacing battery terminals.


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  6. Can water short out an alternator?

    Water can damage an alternator, but does not normally cause it to short out. Automotive alternators operate at less than 15 volts, and water does not readily conduct such a low voltage. Water can damage diodes, cause bearings to fail and promote internal corrosion, all of which can ruin an alternator.
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  7. Can you help? I have an old Suburban and the left turn signal flashes very fast, while the right flashes at normal speed?

    Rapid flashing of the turn signal, on this vehicle, often shows one of the turn signal lamps are not operating. Check all the bulbs in the left-turn signal circuit. I have also seen quite a few failures of the circuit board that holds the rear tail lamps.

    Examine the plastic around the sockets in the circuit board. Often the center socket will be discolored. Replacement of the circuit board will normally get the lights flashing at a normal speed. Many technicians suggest to prevent future occurrences, replace the bulbs with an LED type of the same number. The LED bulbs draw lower amperage and may last longer.


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  8. Codes P0174, P0171 and P0300 were set on my GMC Sierra. I had the intake gaskets replaced and 18 months later I have the same codes again. Why would this keep happening?

    The 4.8L, 5.3L and 6.0L General Motors V8 engines had a good deal of problems with intake gasket leakage. We have found the fasteners that secure the intake contribute to the problem. When they are not replaced, with the intake gaskets, the problem will soon return. Another possibility is, the intake is warped too badly for the gasket to seal.

    For more information, please see our Detailed Topic, GM V8 Rough Idle When Cold.


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  9. Does being low on oil make a check engine light come on?

    Some vehicles will set the check engine light with low oil pressure, because it interferes with engine operation. As a general rule, the check engine light means the vehicle computer system has encountered a problem it cannot resolve. This is an early-warning system to inform the driver a problem is occurring or is about to occur. Engine functions such as oil level, oil pressure and temperature generally have their own separate warning indicators.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.


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  10. Does my replacement battery need to be the same size as the original?

    Batteries have several specifications that make them work best in a particular vehicle. For instance, they have a specific number of cold cranking amps or CCA. A lower CCA battery may not crank the vehicle in all conditions. The correct amount is good, but more is NOT better. As CCA goes up, reserve capacity or RC goes down. Too many CCA will have insufficient RC.

    The size limitations, terminal type and placement, vented and non-vented designs, hold down types are also critical.

    Automotive batteries are normally assigned group numbers. A group number specifies the size and electrical characteristics of a battery. Matching the group number on the replacement battery with the original will greatly help in getting the correct battery.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die.


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  11. Does the check engine light come on for automatic transmission problems?

    Most vehicles built after 1996 have sensors in the automatic transmission that allow the computer to monitor operation. A few things monitored are slippage, missed shifts, loss inputs, excess pressure adaptation and solenoid functions. OBD-II transmission codes will normally be numbered P0700 to P0799 and P1700 to P1799.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.


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  12. Does the check Engine light come on when my vehicle needs routine maintenance?

    The check engine light, more properly a malfunction indicator light (MIL) is not designed to track maintenance. Its purpose is to monitor the computer operating system and sensors that run a vehicle. When the light illuminates, a malfunction has occurred and needs to be addressed as soon as possible.

    Neglecting maintenance for an extended period can cause a malfunction, in which case the light could come on. For instance failure to service an automatic transmission can cause it to fail, which could turn on the light. Properly performed, maintenance is a small investment to prevent major problems.


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  13. Every so often, when I try to start my Toyota, I just get a click and it does not crank over. After a few tries it cranks fine. I have replace the battery and checked the cables.

    The most likely cause would be the starter contacts. These contacts act as a solenoid and are inside the starter. They can be replaced without replacing the entire starter. As a diagnostic test, connect a volt meter between the battery terminal on the starter and ground. If there are 12 volts present, as the key is held in start position, and the click occurs, the contacts are likely the cause.

    For more information, please see our Detailed Topic, Why Does The Engine Not Crank?


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  14. How can I be sure I get the correct replacement vehicle battery?

    The Battery Council International (BCI) assigns a group number to batteries that identifies their key size, post type and capacity characteristics. Matching the group number on the old battery with the replacement will ensure the battery will fit. The group number does NOT take quality of the product into account, however. When choosing a replacement battery, the advice of a trusted professional can be quite valuable.


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  15. How can I check my fuel gauge to see if the problem is the sender or the gauge?

    A fuel gauge that does not work at all, on an older vehicle can often be tested by removing the wire that connects to the sender unit. First remove the wire and then ground the wire. If the gauge now moves, the problem is in the tank. With newer vehicles and intermittent problems, it is significantly more difficult and almost impossible without training and instruments to read the digital feeds. On these vehicles, a scan tool is used to read the input from the tank and to check the function of the gauge.


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  16. How can I tell how many amp alternator I have with out taking it off?

    On any relatively modern vehicle, the vehicle identification number (VIN) can often be used. Anyone with access to a VIN parts database can find the options of the vehicle. Without this, the amperage rating is sometimes stamped on the case of the alternator, though it can be difficult to read. The vehicle option placard may also list the alternator option. These can be found on the driver's door, on most Chrysler's products. The option decal is often on the driver's door pillar on Ford's products. With General Motors, it may be in the glove box, truck or on the spare tire carrier.


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  17. How does the check fuel cap light work?

    The check fuel-cap light is an extension of the standard on board diagnostics [OBD] of the vehicle. The fuel cap is part of the evaporative emissions system. The engine computer tests to be certain the system is air tight. It does this by drawing a vacuum and seeing how long it will hold. If the system cannot achieve a vacuum, it assumes there is a gross leak and sets the check fuel-cap light. The system can be misleading as a number of other things can cause the same symptom. If tightening the cap does not rectify the problem, the evaporative emissions system should be checked.

    Please see our Detailed Topic Evaporative Emissions Systems and Fuel Caps for more information.


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  18. How does the warranty on a battery work?

    Batteries may carry one or two warranties. The first is free-replacement and not available on all batteries. There will be a period of time in which the battery will be replaced without charge, if it fails. This period is normally six-months to two-years. This is an actual warranty.

    The second type is the more common pro-rated warranty. Often these are little more than over-priced insurance, added to the cost of the battery. For instance the battery may have a six year warranty. If it fails in two years there is a cost per month for the time the battery was used. With pro-rated warranties, the cost of replacement often exceeds the price of a new battery, if the battery is a few years old. Generally, buying a battery with over a five year warranty is a waste of money.


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  19. How many amps should my starter draw when cranking?

    The exact amount will vary from vehicle to vehicle and even on the same vehicle from cold to hot temperature. Cranking several vehicles in the shop and measuring, provided an average of around 185 amps. This is with gasoline engines and at 70 degrees Fahrenheit. The highest was around 200 amps, and the lowest was 175, so I feel this is pretty typical.

    For more information, please see our Detailed Topic, Why Does The Engine Not Crank?


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  20. How much of a drain is the alternator on the engine?

    Alternators take about one horsepower for twenty-five amps of output. A 125 amp alternator would require about five horsepower, when at the full charge. Because of this high-power consumption and because of the heat generated, modern vehicles regulate output to just above what is needed.


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  21. I am taking a long trip, can an alternator be tested to determine if it might fail?

    There is no basic test for overall failure. We can inspect the bearings with ultra sound, etc, but there is no guarantee of not having an electrical breakdown. The best protection is to remove the causes of alternator failure.

    Number one and by a wide margin is low grade and old batteries. I replace my battery every three years and have never had to replace an alternator on a vehicle I owned. Weak batteries seriously overwork alternators.

    Second is the belt, if it's old, it will slip and even though it may not make noise, can ruin the alternator. Lastly are the cables. They need to be clean and tight. Loose or corrode cables tend to kill alternators. If the ends are corroded, the cable should be replaced or professionally repaired [hydraulically crimped on ends]. Temporary, bolt on ends are a kiss of death to alternators.

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  22. I had my timing belt replaced and after leaving the shop my ABS light came on after 10 miles. I returned to the shop and was told the ABS module had failed. I am very suspicious, what do you think?

    That is quite a coincidence. Still things do happen and it is possible the two incidents are not related at all. I would discuss my concern with the original shop and tell them you would like a second opinion. Select a second shop agreeable to both of you and have them diagnose the problem. Should the problem not be related to the original work, and other work was satisfactory, I would return to the first shop for repairs.

    Should a problem be discovered relating to the original repair, the first shop should be informed before any repair is made. This will give them an opportunity to inspect the damage and should make collecting for correction much easier.

    In the Detailed Topics section there is an article entitled When Things Go Wrong that has a lot more information on this topic.

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  23. I had the rack and pinion replaced in my vehicle and when I picked it up the air bag light was on. The shop says it is not related to the work they did. Could this be a coincidence?

    Have the air bag system checked and see which code is present. If the clock-spring is damaged it is likely related to the rack and pinion job. If the steering wheel is turned with the rack and pinion removed or if the rack is not properly timed, the clock-spring can be damaged. If the fault code shows a problem in a non-related area, it could be coincidental.
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  24. I have a light that says SIR, what does it mean?

    SIR means supplemental inflatable restraint, more commonly called an air bag light. The system monitors speed and rate of deceleration to determine when the vehicle has been involved in a collision. Generally an impact at 12 MPH or more and within 12 degrees of center will cause the front air bags to deploy.

    The system also monitors the status of the components, of which there are several. Very basically, there is are frontal crash sensors, arming sensor(s) bag modules, a clock spring assembly, wiring harness and an electronic control unit with backup power. Other systems also have seat sensor and active seat belt monitors included. When the key is turned on, the system goes to a self test mode and the light will remain on for a few seconds. Once the components are confirmed okay, the light goes out, signaling the system is ready to operate.

    Failure of any component to test properly will cause the light to come on. A light on indicates a fault has been detected and the system may not deploy in a collision. Newer systems also have side air bags that deploy in side impact situations. There are several dozen things that can cause the light to stay on and only by diagnosing the system with proper tooling can the reason be determined. The problems can range from loose connections to module failures and cost vary widely depending on the problem.

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  25. I have an odor, almost like rotten eggs coming from under the hood of my vehicle.

    One source of such an odor is an over-charged battery. This may also be accompanied by corrosion on the cables as acid is often boiled out of the battery. When batteries over-charge, the fault will be in the charging system. The alternator or the control circuit will have to be checked to isolate the cause.

    Another common source of rotten egg odor is the catalytic converter. This will normally be noticed coming from the exhaust.

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  26. I have an older Chevy pick up that runs fine, but my air bag light stays on. What does this mean?

    The air bag light, often labeled SIR for supplemental inflatable restraint, indicates the ability of the air bag to deploy in a collision. Being on, indicates that it may not inflate when needed and in some cases that it could deploy when it shouldn’t.

    First check to see if the fuse is blown and replace it if needed. If this is the problem the light should come on for a few seconds when the truck is started and then go out and stay off. If the light remains on, or if the fuse is not blown, we can check the system and repair it for you. There are literally hundreds of possible causes of failure from a loose connection to a bad diagnostic module.

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  27. I have code P0305, P0307 and P0132 on my Chevrolet pickup and it idles roughly. I have changed the O2 sensors, spark plugs, wires, distributor, cap and rotor. The same codes are still present. A friend says it might be the head gasket.

    Parts changing is a VERY expensive way to attempt to correct a problem. Paying for an accurate diagnosis would have been far less expensive. The diagnostic trouble code (DTC) P0305 and P0307 indicate a misfire on cylinders five and seven. Code P0132 indicates voltage too high from the left bank O2 sensor.

    Voltage too high means the left sensor is detecting too much unburned fuel in the exhaust. This might be expected with a misfire on the two cylinders, which are also on the left bank. Odds are the O2 sensor was fine. Specific cylinder misfires will be related to things specific to those cylinders. Swapping the spark plugs and wires with a cylinder that was not missing and checking the results would have revealed they were not the cause.

    A logical step might be to check the engine compression. If compression is good and there is no evidence of coolant on the plugs in cylinders five and seven, a head gasket is not likely. A shop might run a fuel injector balance test as the next step. A stuck injector, leaking injector body or bad fuel regulator could account for all three codes.

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  28. I have no brake lights and the shop is telling me it is the turn signal switch. How can the turn signal switch keep the brake lights from working?

    Many vehicles use the same wiring and bulbs for the turn signals as they do for the brake lights. The turn signal switch cancels the brake light on the side selected by the turn signal, allowing it to flash. The turn signal switch is a possibility, especially if the high-mount brake light still operates.

    For other things that keep brake lights from operating properly, please see our Detailed Topic How To Diagnose Brake Light Problems.


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  29. I have one turn signal bulb that keeps going out. I replace it and about six months later it goes out again.

    Repeated failure of a single light is often caused by a bad lamp socket. This is particularly common on the push in type sockets that are not spring loaded. Replacement of the socket will often cure the bulb issue.

    For more information on light sockets, please see our Detailed Topic How To Diagnose Brake Light Problems.


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  30. I have seen code readers advertised in several magazines. Can I save money by buying one of these and fixing my own vehicles?

    Code reader can be of limited help as long as you also have the information and understand the operation of the system you are trying to repair. The diagnostic trouble code (DTC) only gives the computer’s interpretation of the area causing the problem and not a diagnosis.

    For example a code could indicate insufficient exhaust gas recycle (EGR) flow. This does not mean the EGR valve is bad, though that is one possibility. It could also be the sensor that reads the flow, the wiring leading to and/or from the valve and sensor, plugged ports feeding the valve and many other possibilities.

    Code readers do not give bi-directional communication with the vehicles computers which is often needed to isolate the malfunctioning part(s). It might be less expensive and frustrating to form a relationship with a professional shop, have them do the diagnosis and you replace the parts if you like.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  31. I have several weird electrical problems with my vehicle. Where is the best place to start looking?

    With electrical issues we generally always start with the battery and cables. System voltage is critical and weak batteries, loose, corroded or improper cables create far more than their share of problems.

    For even more information on batteries and cables, see our Detailed Topics article, Replacing battery terminals.

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  32. I just bought a used Ford and noticed the fuel gauge wasn't working. What could be the problem?

    The most common causes are either a bad fuel level sender (in the fuel tank) or a bad fuel gauge. If you are handy, locate the signal wire coming from the fuel sender. If you ground the wire the gauge should move to one extreme. If it does the gauge is likely okay and the sender is more likely the issue. If you don't care to try this, with a Ford scan tool, the gauge can be cycled and the sender output tested. This likely would not cost a lot to have tested.
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  33. I put a locking gas cap on my car and now the check engine light comes on?

    There are a great many designs of gas caps in common use. Different sealing areas, diameters, thread pitches and attachment styles. You may have gotten a cap that does not properly fit your fuel filler neck. If a cap does not form an air-tight seal, the evaporative emissions [evap] system will turn on the check engine light to indicate the fault.

    Please see our Detailed Topic Evaporative Emissions Systems and Fuel Caps for more information.

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  34. I was involved in a rear collision and the next day my check engine light came on. The code indicates EGR failure, could this be related to the accident?

    The EGR (exhaust gas recycle) system is attached to the exhaust pipe on many vehicles. If the pipe were damaged, bent, broken or restricted it could cause an EGR fault. Excessive movement of the exhaust might also cause an EGR problem. EGR systems do also just fail at times and it may not be related.

    A competent technician should be able to quickly identify the problem and by the nature of the failure determine if it relates to the collision.

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  35. In the last few days a red light that says BRAKE comes on, remains for a several seconds and then goes back off. It seems to be related to turning a corner and accelerating.

    Common causes of such behavior are low brake fluid or a bad fluid level sensor. Check the fluid level and if low top it off with the specified fluid from a new and unopened container [also see below]. If the light persist the sensor can be temporarily disconnected, as a diagnostic procedure. If the light now stays out, the sensor could be at fault. It should be checked by a professional or replaced, knowing there could also be other problems.

    It is very important to fully check the braking system when fluid is low. There could be a leak or the brake material could be worn. It is not normal to have to add brake fluid and low fluid always indicates another problem.

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  36. Is hot weather or cold weather worse on a car battery?

    The answer is both. Temperature extremes of either type tend to kill batteries. A good deal of research points out that high temperatures actually kill the battery and low temperature reveals the damage.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die.


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  37. Is it possible for a fuse to look okay and still be blown?

    Yes, a fuse may not appear to be bad, yet have failed outside of the visible area. A volt-meter is a quicker and more certain method when checking fuses.

    For more information on checking fuses and relays, please see our Detailed Topic, How to check fuses and relays.


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  38. Is there a way to disable the check engine light on my Suburban?

    There is no way to disable the check engine light (MIL), nor any logical reason to try, in my opinion. On any post-1996 vehicle, the MIL is not the problem, it is merely indicating a problem. This system is fully integrated into the computer management of the vehicle and can check for about 2000 improper conditions. The MIL is simply trying to alert the driver to a condition that may cause more damage. In almost every case, early repair saves a great deal of additional expense.

    Another way to think about it might be, a smoke alarm in a high rise building. The alarm brings attention to a bad situation. It does not say what the situation is nor what it will take to correct. A smoldering trash can may be quite easy to extinguish. Ignoring the alarm may result in loss of the entire building or worse.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  39. My ABS brake light is on but there are no symptoms.

    An ABS warning light indicates the anti-lock brake system is not in an operable condition. This could be due to component failure, cut/disconnected wiring or parts in the system out of the proper range. Under normal operation, symptoms will not always be noticeable. Symptoms may only become apparent when the vehicle is in a brake lockup situation. When the light comes on, a code(s) will generally be stored. Retrieving the code(s) will identify the area of the system that is causing the problem. From there, testing of components is necessary to identify and correct the actual problem.
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  40. My battery cables are corroded, should I replace the ends with bolt on terminals?

    Bolt on replacement terminals are called emergency temporary terminals for good reason. They are a temporary repair at best and should be used only in an emergency. As with everything a diagnosis is in order, before repair.

    First be sure the battery is not leaking, causing the corrosion. Leaking batteries are very common and the acid causes severe damage to vehicles. It can easily eat holes through brake, air conditioning, transmission lines and worse. If the battery is found to be leaking it should be immediately replaced and all traces of acid neutralized with baking soda and water.

    Next check the cables to see if acid has “wicked” it’s way up the cable. With a sharp knife split the insulation back a few inches. If there is a white powdery appearance to the cables they must be replaced. If not they may be able to be repaired. Some cables are very expensive and repair is more practical than replacement.

    With the proper equipment, a new end can be crimped onto the existing cable. Done properly this is a permanent repair and works as well as a replacement cable. AGCO can handle this repair for you if you would like.

    For even more information on batteries and cables, see our Detailed Topics article, Replacing battery terminals.

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  41. My battery terminal keep corroding and I was told my battery is leaking. My car starts fine, do I need to replace the battery?

    Leaking battery acid is extremely corrosive and can do a great deal of damage to wiring, air conditioner lines and body panels. With the low cost of a battery, relative to the possible damage, it make no sense to not replace the battery.

    For more information on potential problems from battery leakages, please see our Detailed Topic The Cost of Battery Terminal Corrosion.
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  42. My brake lights are not working. How can I test for the brake light switch?

    First depress the pedal and see if the third or center-mounted brake light works. If it does, the fuse and switch are likely okay. If not, check the input and output on the switch leads with a volt meter. If there is voltage going in, but not coming out, the switch is likely bad. If there is no voltage going in, check the feed circuit and fuse.

    For more information on brake light problems, please see our Detailed Topic How To Diagnose Brake Light Problems.


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  43. My check engine light came on about a year ago. The car still runs well but the light is still on. Is this anything to be concerned about?

    Most definitely! Check engine lights do not come on without a reason. The one light can indicate approximately 2,000 different malfunctions, depending on the vehicle. Many malfunctions are initially quite minor, for instance a vacuum leak. If left unattended they can turn into major problems however.

    Another problem, if the light is on, even due to a minor issue, and another problem occurs, you will not know. I would advise you to have the problem addressed immediately.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  44. My check engine light came on and a friend told me I should disconnect the battery and see if it goes off? Would you recommend that I do this?

    I would never recommend disconnection of the battery to turn off a malfunction indicator lamp (MIL). Disconnecting the battery may temporarily turn out the light on some vehicles, but it also destroys the data a technician will need to repair the vehicle. Loss of this data can make correction of the original problem that caused the light to come on much more expensive.

    Worse, other data that led up to the failure, that turned on the light can greatly speed the time of repair and reduce the cost substantially. This data and any fault codes are also loss when battery power is disconnected. Only a trained technician, after recording the needed data, should clear fault codes.

    For even more information on check engine lights, see our Detailed Topics article, Failing State Inspection.


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  45. My check engine light came on and after repair the invoice listed code P0304. Does this code have a specific meaning?

    Yes, this is a generic on board diagnostics II (OBDII) code for a misfire on cylinder number four. Generic codes are set by the Society of Automotive Engineers (SAE) and are always five characters long. As a very general overview and currently, the first character is indicates which system logged the code.

    P = Power train (engine/transmission, etc)
    B = Body (Air conditioner/heater, body controls, etc)
    C = Chassis (Steering, ride controls, etc.)
    U = Undefined (Network, etc)

    When the second character is 0 it indicates a generic code. A higher number indicates a manufacturer specific code and can vary from one make to another or even among makes.

    The third character indicates the area that caused the code to set.

    1 or 2 = Fuel or air metering
    3 = Ignition or engine misfire
    4 = Auxiliary emissions controls
    5 = Vehicle speed controls and idle controls
    6 = Computer output circuits
    7 or 8 = Transmission

    The forth and fifth digits or the specific condition that caused the fault. In your example the P indicates a power train concern, OBDII generic, misfire of cylinder number four. This does not indicate what caused the misfire only that it has occurred. With this information and additional testing a technician can determine the problem.

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  46. My check engine light came on and stayed on all day. The next day it did not come on and has not come on in two days. Is this still a problem?

    The malfunction indicator lamp (MIL) may often act in this way. The computer test the system and when it finds a problem turns on the MIL to alert the driver. When the ignition key is cycled the code is removed from current memory but retained in history. Depending on the problem and the vehicle, this may cause the light to go out. The light may then stay out until the computer runs this particular test again, which can take several days under certain conditions.

    Complicating the strategy further are two trip and three trip codes. These faults must occur two or three times in a single key cycle to turn the MIL on. Several short trips can be made and never meet the conditions for light illumination, even though a problem exist. The vehicle should be checked by a professional technician as soon as possible.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  47. My check engine light is on and I am told it is the EGR valve. Can I still drive the vehicle with the EGR valve not working?

    EGR or exhaust gas recycle lowers emissions and helps to prevent engine-damaging detonation, pinging and valve knock. The EGR valve opens when commanded and allows exhaust gas to enter the combustion chamber. This helps to cool the temperature and prevents spontaneous combustion of the fuel air mixture. Engine damage can result and there may be a loss of performance without the EGR system.

    For more information on exhaust gas recycle or EGR valves, please see our Detailed Topic How does and EGR valve work.


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  48. My check engine light was on so I had a friend clear the codes. When I went to get an inspection sticker I was rejected because the readiness test were incomplete.

    When the codes are cleared on an OBDII vehicle, the I/M test are also cleared. This means the vehicle computer must test and pass all involved components. Until these test have completed and passed the readiness status will indicate incomplete. If a test fails, the check engine light will come back on.

    For even more information on check engine lights, see our Detailed Topics article, Failing State Inspection.

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  49. My check engine light was on, I had it repaired then it came on again. I returned to the shop, had more repair done and now it is on again. This is the third time in a year, it seems the shop is not doing something right.

    Each time the light comes on there should be a diagnostic trouble code (DTC) stored in memory. It is important for the shop to list these codes on your invoice when repairs are made. With this information it should be easy to see if the same problem has recurred or if each visit is actually a different problem.

    This is not necessarily a problem with the shop. Later model vehicles can have over a thousand causes for a check engine light. As annoying as it is, you must remember there is only one light and many problems that can turn it on. Another issue is that most sensors [a prime cause of problems] have a service life of about 100K miles. It is not unusual to see several fail at this milage.

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  50. My driver’s side low beam headlight keeps going out. I have changed it three since I bought the car in 60,000 miles.

    Short bulb life, on a single bulb, is almost always one of a few things. First is a loose connection somewhere in the circuit. The connection causes voltage fluctuation, too fast for the eye to perceive. The effect is a shortened life for the bulb. Favorite offenders are the bulb socket, any connector in the circuit and sometimes the switch. The ground side of the circuit is equally important, and a loose ground causes the same problem.

    The second cause is a loose mounting that allows the bulb to vibrate. Excessive vibration will break the filament inside the bulb. Finally, a crack or hole in the headlamp housing allows moisture in, and this will cause the hot bulb to fail.


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  51. My engine would not crank when I turn the key. I replaced the starter relay, it tried to crank, but the relay immediately burned out. What would cause this?

    Connections and relays almost always burn because of excessive amperage flow. First check to make sure the engine and all accessories on it rotate freely. You can check by putting a wrench on the large crankshaft nut and turning the engine by hand. If the engine turns freely and smoothly, I would suspect a shorted starter motor. Have the amperage draw of the motor checked.

    For more information, please see our Detailed Topic, Why Does The Engine Not Crank?


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  52. My Maxima's starter has begun to occasionally miss engaging the ring gear on start-up and makes a loud ZING! Which rebuilt starter brand is the best to use?

    First, be certain the starter is the problem. Nissan has a rebuilt starter sold through their dealers and I have found it to be of very high quality. I have seen people have poor results with other rebuilt brands and we replace them with Nissan supplied starters quite frequently.
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  53. My truck quit running two weeks ago. A friend checked it and told me there was no fuel pressure. I replaced the fuel pump and it ran for a couple of hours and then died again. Do you think this pump is defective?

    Anything is possible, but a flaw in the diagnosis could as likely be the problem. Lack of fuel pressure does not mean the fuel pump is bad or that a bad fuel pump is the only problem. The fuel pump must have power and ground to operate.

    Power and ground at the pump with no fuel pressure would indicate a bad pump. Since you did not mention checking these, I would start with them. A bad fuel pump relay, or a bad wiring harness could prevent power from reaching the pump.

    Some vehicles even have circuits that disable the pump under certain conditions, such as an oil pressure switch. If the switch does not see pressure, it cuts the fuel pump. It might be prudent to test the electrical circuitry before changing any additional parts.

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  54. My vehicle came equipped with ten-ply tires. The tire pressure monitoring system was set for 50 PSI. I would like to reduce the air pressure to improve ride. Can I do this without making the warning light come on?

    It is not advisable to ever go below the Vehicle manufacturers recommend tire pressure. It is normally calculated with ride as a primary concern and should be considered the minimum allowable. Tire pressure monitoring systems (TPMS) take this into account and will illuminate if pressure is set below the recommended amount.

    Also see our tire pressure article for a great deal more information.

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  55. My vehicle failed the State emissions inspection and I was told it was because my cigarette lighter did not work. How can that be?

    In order to test the onboard emissions system, many States connect an electronic device to the vehicle. These connector used is often powered through the cigarette lighter or accessory plug. If the device does not show a power source, it will often register a failed test. We repair quite a few lighters and accessory plug systems for this reason.
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  56. My vehicle was recently wrecked in the front but the air bag did not deploy. Is this a defect?

    Air bags or supplemental inflatable restraints (SIR) only deploy under certain conditions. For instance the impact normally has to be in excess of 12 MPH. It may also have to be within so many degrees from center of the vehicle, (e.g., an impact 20 degrees off center may not deploy the bag and one 5 degrees may.) These systems are quite well tested and an onboard computer monitors their status. Chances are if the SIR light was not on, indicating a fault, the impact did not meet the criteria for deployment.
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  57. Only my top brake light is working and not the two main brake lights. The turn signals work and the hazard flashers work as well. All fuses are okay.

    A likely cause may be the turn signal switch or the connectors on it. If the hazard lights work, the wiring, bulbs and sockets are working. If the third light comes on, the fuses and brake light switch are working.

    The turn signal switch interrupts the brake light, on the side that is flashing. If it did not, the light could not flash. When the switch or connection fails, it can interrupt the lights when it should not.

    For more information on brake light diagnosis, please see our Detailed Topic How To Diagnose Brake Light Problems.


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  58. Recently I had to have head gaskets replaced on my vehicle. The shop said the car had been over heated, but the warning light never came on. Is this possible?

    Many times overheating is caused by low coolant, resulting from leakage. The coolant reservoir replenishes the radiator, until it runs empty. With no reserve coolant the radiator runs low and the coolant level drops in the engine. Unfortunately, on many vehicles when this happens the electronic coolant temperature (ECT) sensor may no longer contact the coolant. Under these conditions the engine can overheat and not indicate this to the driver.

    Warning lights and gauges are very handy reminders, but are not error-proof. A quick inspection of fluid levels, on a regular basis is a very good idea. Also be aware, that once the coolant reservoir gets empty, filling it may no longer fill the radiator. The syphon effect is loss once the radiator gets low. Allowing the vehicle to completely cool and filling the radiator with the proper pre-mixed coolant is necessary to restore operation. It is also NOT normal for the reservoir to require additional coolant. A low reservoir indicates a problem.

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  59. Recently my vehicle air conditioner was repaired. Shortly after picking the vehicle up, the check engine light came on. Could this be a coincidence?

    It could be, there are almost 2000 possible reasons a check engine light can come on. It could also be related to the repair. They may have inadvertently left off a vacuum hose or possibly left a sensor disconnected. If so, the repair should be very minor and no charge to you. By having them retrieve the diagnostic trouble code (DTC) in memory, it should be reasonably easy to establish if the problem could be related to the repair.

    Most quality shops would welcome the opportunity to correct the mistake. If the shop feels it is not related to their work and you feel it may be, a second opinion from another qualified shop may be in order. In the Detailed Topics section there is an article entitled When Things Go Wrong that has a lot more information on this topic.

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  60. Several alternators have been replaced on my vehicle. Is this just poor quality parts?

    Very poor quality parts are quite common and that is a possibility. Batteries and improper cables can also cause alternators to fail. An undersized battery or one that is weak can cause the alternator to work much harder than normal. Poor cables can have high resistance and quickly ruin an alternator as well as several other components. Finally a weak belt tensioner or loose drive belt can slip and damage an alternator.

    For even more information on batteries and cables, see our Detailed Topics article, Replacing battery terminals.

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  61. Some part stores offer to read codes for free when a check engine light comes on. What is the advantage to having a professional diagnosis?

    This practice is popular with part stores because it sells a lot of parts. Most professionals see people each week who have spent hundreds on unneeded parts from this. Many people learn the hard way, a professional diagnosis is the least expensive way to fix the problem.

    A diagnostic trouble code (DTC) only shows why the computer turned the light on and not what is wrong with the vehicle. For instance a vacuum leak, bad air flow meter, clogged injector, bad coil, bad plug or many other things can set an oxygen (O2) sensor code. The sensor is out of range because of other factors in the engine and replacing it will have no effect. Save money, a free diagnosis is much too expensive.

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  62. The ABS light came on and the wheel speed sensor was replaced. Less than a year later the light came back and the sensor was again replaced. Two weeks later the light is back on. Why does the sensor keep failing?

    Likely the sensor does not keep failing and the actual cause of the problem is being mis-diagnosed. For instance a bad connector could cause the ABS light to come on and display a sensor code. Replacing the sensor and re-connecting might clear the problem temporarily. Eventually the connector again may lose contact and the cycle repeats. Many things can cause a sensor code other than the sensor. Best might be to try another shop, giving them the full history of what has occurred.
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  63. The air conditioner blower in my vehicle quit working. I replaced the blower resistor and it worked for a while and quit. Could the switch be bad and how can I check it?

    The switch does fail as well as the connections going to it. With a volt meter power going in can be tested. If there is power going in and none coming out, the switch is bad. A physical inspection will normally reveal burned connections.

    My experience has been, when switches and connectors burn, the motor is the normal cause. As motors age, they can start drawing more current to operate. If the motor pulls much in excess of ten amps, it may burn the up-line components. In every case where I see repeat resistor and switch issues, the problem is normally resolved by also replacing the blower motor.

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  64. The anti lock brake light is on in my vehicle, but no codes show with a code reader.

    Modern vehicles have several computers. Some have up to twenty different modules. They communicate with one another but do not always share diagnostic information. For instance an ABS code may be stored in the body control module (BCM) and not the power control module (PCM.) Retrieving codes from body, transmission, air bag, climate control and other modules normally requires original equipment manufacturer’s level tooling. These cost several thousand dollars and different tools are required for different makes and even different years within a vehicle line. It will likely be necessary to refer this problem to a professional with the proper tooling.
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  65. The battery in my vehicle goes dead over night. If I disconnect the cable from the battery and reconnect in the morning it is good. What could cause this?

    This sounds like a parasitic draw on the electrical system. That is, something is staying on and drawing current when it should not. There are countless possibilities, some of the more common are glove box lights, trunk lights, and accessories.

    First turn everything off in the vehicle that can be turned off and disable the door light switch, if the door needs to be opened. Diagnosis begins with connecting a sensitive amp meter inline with one of the battery terminals and it’s cable. If the meter reads current flow above a few hundredths of an amp there is a problem. Remove fuses from the fuse box(s), one at a time until the meter drops. This will identify the circuit with the draw.

    Once the circuit is identified you will need a wiring diagram to learn what is on that circuit. Each component would then need to be disconnected until the draw diminishes. Once identified the component can be repaired or replaced as needed.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die.

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  66. The brake lights on my Honda Accord are staying on, even though the pedal is not being pressed. What would cause a problem like this?

    There is a small stopper on the brake pedal, where it contacts the switch. In time the rubber may deteriorate and the stopper may fall out. The pedal no longer contacts the switch, so the brake lights are not turned off when it is released.

    For other things that keep brake lights from operating properly, please see our Detailed Topic How To Diagnose Brake Light Problems.


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  67. The center brake light on my vehicle lights but the regular brake lights do not. The fuse, bulb, sockets and brake switch all test good. What could be the problem?

    Brake lights often route through the turn signal switch and use the same bulbs. If this is the case check the input and output of the turn signal or multi-function switch. This is a common failure point.
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  68. The check engine light came on and a part store told me it was the gas cap. I replaced the cap and the light is still on. How can this be?

    Check engine light diagnostics is a complex field and reading a code in memory is not determining what is wrong. There are several dozen things that can cause any given code and only by proper diagnosis can the actual problem be determined. Swapping parts is very expensive and not at all effective.

    Please see our Detailed Topic Evaporative Emissions Systems and Fuel Caps for more information.


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  69. The check engine light is on in my Yukon and I was told the intake manifold is leaking. I can see nothing leaking under or around the vehicle.

    Most likely the shop is speaking of a vacuum leak and not a fluid leak. When an intake manifold leaks vacuum, air is drawn through the leak and disturbs the fuel/air mixture. This can result in a check engine light with no physical leak that can be seen.

    For more information, please see our Detailed Topic, GM V8 Rough Idle When Cold.


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  70. The Check Engine light on my Ford is on. I took the vehicle to a part store and was told I needed an EGR valve. I bought the valve, replaced it, but the light still comes on.

    The Check Engine or more properly Malfunction Indicator Light (MIL), is a symptom indicator. The Diagnostic Trouble Codes (DTC) stored in memory are not to be taken literally, only as an interpretation of the circuit creating the problem.

    In this case the DTC may have indicated something like Exhaust Gas Recycle (EGR) flow insufficient. This does not mean the EGR valve is bad. It means the engine computer sees a problem with the system. This problem could be the result of several things.

    For instance the sensor that tells the computer that the valve is flowing could be malfunctioning. The hoses that provide input to the sensor could be bad. A connection could be loose or the passages that flow exhaust to the valve could be plugged. These are only a few of the possibilities and listed to make a point.

    The point is, it is much less expensive to have the system properly diagnosed. Paying for a professional diagnosis would have saved the cost of the EGR valve. Replacing parts, without knowing the actual cause of the problem is expensive and seldom solves the problem. Some part stores advocate this approach, for obvious reasons.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  71. The check engine light was on in my car. A parts store cleared the codes but my car still failed inspection.

    Whenever a problem occurs on the vehicle that can affect emissions, the check engine light is set. At the same time a diagnostic trouble code (DTC) is stored in history. Clearing the code will not repair the cause of the problem. When the memory is cleared, the registers for test results are also cleared. When this happens, the vehicle will begin testing every component and marking it as passed or failed. If you attempt inspection before the test are complete, the vehicle will fail for that reason. If the original problem has not been corrected, the light will again come on when the test is run.

    For even more information on check engine lights, see our Detailed Topics article, Failing State Inspection.

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  72. The company I work for rents a van from a large rental firm. The check engine light is always on and when we bring it to the rental companies attention, they simply clear the code. The next day the light is back. Should I be concerned?

    I feel you have every right to be concerned. The check engine light indicates an emissions or running problem with the vehicle. Ignoring the warning is irresponsible and possibly illegal. Many areas have laws against driving with a check engine light. When you further consider the cost of [premature] replacement of the vehicle is covered by the cost of rental you should be concerned. A letter to the agency manager with a CC to the main headquarters and your manager may help. If not, I would select another company from which to rent.
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  73. The fuel gauge on my Impala shows 1/4 tank but the driver information center reads low?

    Both the gauge and the information center read off the same sender unit. If the sender were bad, both would read improperly, but agree in reading. A likely cause would be the gauge in the dash. You could verify this by filling the tank and noting the amount of fuel taken. Compare the amount added to the capacity of the tank. If considerably more than three-quarters of the fuel capacity can be added, the gauge is the likely problem. If very close to three quarters fills the tank the problem would more likely be in the drivers information center.

    Please see our Detailed Topic article GM Dash Gauge Failure for far more details.


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  74. The low coolant light came on in my vehicle and the coolant reservoir was empty. I filled the reservoir but the light is still on. Do you think the level sensor is the cause?

    The coolant level sensor could be the cause, but you should also physically verify the coolant level. When a cooling system gets low it can draw air into the system. Once air has entered the system the reservoir may no longer function to fill the system.

    Wait until the vehicle is completely cooled and remove the radiator cap. If the level is low, fill it with the specified coolant and distilled water, premixed half and half. Replace the cap and see if the light is out. If not, the warning light problem is likely with the level sensor circuit.

    Whether the light goes out or not the vehicle needs to be tested and the source of the leak repaired. The system being low indicates it is leaking and this can cause severe damage if left unattended.

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  75. The oil pressure gauge in my Chevy Suburban moves from zero to maximum when I start the truck. Could this be the gauge?

    More likely if the gauge returns to zero when the engine is turned off the gauge is not the fault. The oil pressure sender unit on these vehicles is a very common failure item and a more likely cause. Temporarily unplug the sender unit and if the gauge falls to zero, the sender is more likely the cause.

    Please see our Detailed Topic article GM Dash Gauge Failure for far more details.


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  76. The oil pressure gauge on my GMC Sierra is stuck all the way on high. Do I have to take this to a GM dealership?

    The 2003 through 2006 GM truck instrument panel cluster (IPC) was under recall up to 70,000 miles. In order to have it repaired under the recall, you would have to return to a GM dealership. If you are out of the recall mileage, any independent shop can make the repair for you, often at a lower cost.

    Please see our Detailed Topic article GM Dash Gauge Failure for far more details.

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  77. The oil pressure light came on in my car while I was driving. I stopped checked the oil and it was full. When I started again the light was out but later came on again, does this sound like a major engine problem.

    Not necessarily, but do not continue to drive the vehicle or it may become one. The first step in diagnosing the problem is to verify the oil pressure with a mechanical gauge. If the pressure is within specifications the problem could be a simple as a bad oil pressure sender unit.

    If the pressure is below specification it is imperative to determine and repair the cause before driving the vehicle. Severe damage occurs very rapidly when oil pressure drops.

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  78. The speedometer of my Chevy Suburban often sticks and reads improperly. I was told this was under recall, but the dealership told me it had expired. What is the term of the recall?

    The 2003 through 2006 GM truck instrument panel cluster (IPC) is normally under recall for up to 70,000 miles. This may be negotiable for another 10,000 miles, depending on the circumstances. In order to have it repaired under the recall, you would have to return to a GM dealership. If you are out of the recall mileage, any independent shop can make the repair for you, often at a lower cost.

    See our Detailed Topic article GM Dash Gauge Failure for far more details.

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  79. The terminals of my battery keep corroding. I clean them and within a few weeks it has occurred again. Is there a way to prevent this?

    Corrosion as you mention is normally caused by acid leaking around the terminals of the battery. This is easily tested detected with a pH test strip. Just lay it on the battery and if it shows acidic (below 7.0) the battery should be replaced.

    Escaping acid from a battery can do severe damage. Air conditioning lines, transmission lines, the radiator, electrical system and the body of the vehicle can all be damaged by exposure to battery acid. The area of the battery should be thoroughly cleaned with a solution of baking soda and flushed with clean water.

    For even more information on batteries and cables, see our Detailed Topics article, Replacing battery terminals.

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  80. This morning when I went to start my car there was a click, click noise and the engine would not crank over. Do you think this is just the battery or should I have the electrical system checked?

    I feel it unwise to just replace a battery, without checking the electrical system. Many times a dead battery is a symptom of another problem. A weak or bad alternator or even a parasitic draw on the system will result in a dead battery. Replacing the battery may not be necessary and even if necessary may not be the full problem.

    Looking at overall lowest cost, checking the system is a lot less expensive than replacing a battery, only to have it ruined by a bad alternator. Just as bad is replacing a battery to find something else is causing the problem, and the battery was not needed.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die.

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  81. What are the symptoms of a bad alternator?

    Alternators can fail in a number of ways. Most failures result in a lack of charging and an eventual dead battery. Sometimes the internal bearings fail and although they may continue to charge for a while, there will usually be a whining noise. Partial failure of the diodes can also result in current discharge back through though the alternator when it is not turning. Modern alternators are usually controlled by the power control module and are difficult to test without sophisticated equipment. For that reason, they are sometimes mis-diagnosed and replaced needlessly.
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  82. What do OBDII codes actually mean?

    Generic on board diagnostics II (OBDII) codes each refer to specific systems, components and faults as follows.

    The first symbol
    P = Power train (engine/transmission, etc)
    B = Body (Air conditioner/heater, body controls, etc)
    C = Chassis (Steering, ride controls, etc.)
    U = Undefined (Network, etc)

    When the second character is 0 it indicates a generic code. A higher number indicates a manufacturer specific code and can vary from one make to another or even among makes.
    The third character indicates the area that caused the code to set.

    1 or 2 = Fuel or air metering
    3 = Ignition or engine misfire
    4 = Auxiliary emissions controls
    5 = Vehicle speed controls and idle controls
    6 = Computer output circuits
    7 or 8 = Transmission

    The fourth and fifth digits or the specific condition that caused the fault. For example P0304, the P indicates a power train concern, OBDII generic, misfire of cylinder number four. This does not indicate what caused the misfire only that the computer thinks it has occurred. With this information and additional testing a technician can determine the problem.

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  83. What does a flashing over-drive light indicate?

    Some vehicles use the over-drive light to indicate transmission malfunctions. This is very much the same as the engine uses the check engine light. On some models, when the automatic transmission computer encounters a problems, it flashes to alert the driver. On other vehicles, the check engine light is used for both engine and transmission. When either light comes on, a diagnostic trouble code is stored.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  84. What does the check suspension message on my Lincoln indicate?

    The air suspension system is controlled by a computer that optimizes ride height for handling, ride and tire life. When the system has an electrical malfunction, the check suspension message will be displayed. Unfortunately, the system only monitors the electrical functions and not leaks. Many times, electrical failures, such as a bad suspension air pump, are caused by over-running the pump, due to a leak.

    For more information please see our Detailed Topic Ford Air Suspension Problems.

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  85. What does the dash gauge marked RPM do?

    The gauged marked RPM is a tachometer and measures the revolutions per minute the engine is turning. This is helpful in knowing when to shift and as a diagnostic gauge to check vehicle speed against engine speed.

    For more information on the gauges on the dash, please see or Detailed Topic, What Do The Gauges on The Dash Mean.


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  86. What does the light labeled “Check Engine” indicate?

    The check engine, more properly malfunction indicator lamp (MIL) means one of the vehicle’s computers has encounter a situation it cannot handle. It does not check the oil, coolant, battery or maintenance due.

    On a modern vehicle there are over 2000 things that can make the light come on. A sensor that is out of range, not reading or disconnected. A vacuum line that is disconnected or plugged. An engine taking too long to warm up or a plugged fuel injector. Even a fuel cap not sealing tightly can illuminate the MIL.

    This is the vehicle’s way of letting you know a situation exist that will cause a problem. Special tooling allows a trained technician to determine the cause and correction needed. Ignoring the MIL, even if the vehicle seems to be running fine will almost always result in a far worse problem or breakdown.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  87. What does the term OBDII mean in reference to my vehicle?

    OBDII stands for on board diagnostics II and refers to a standardized system administered by the Society of Automotive Engineers (SAE). In the shop it is often used in reference to diagnostic trouble codes (DTC) used to help determine what is wrong with a vehicle.

    For even more information on check engine lights, see our Detailed Topics article, Diagnostic Trouble Codes.

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  88. What is a starter solenoid and how does it work?

    The starter solenoid is a magnetic switching device. It allows a small amount of current, controlled by the ignition switch, to start the vehicle. When the ignition switch is turned a small current activates an electromagnet. This magnet closes heavy contacts that allow almost 200 amps to flow to the starter.

    For more information on starter solenoid operation, please see our Detailed Topic, Why Does The Engine Not Crank.


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  89. What is an automotive O2 sensor used for?

    Oxygen sensors help control fuel mixture and reduce emissions. They determine how much oxygen is needed to completely oxidize any fuel remaining in the exhaust. Unburned fuel requires more oxygen and increases the voltage output. The computer sees this as a rich mixture and with other sensors reduces the time the fuel injector remains open. This causes the fuel air mixture to lean out or have less fuel, per air volume. Less fuel in the exhaust takes less oxygen to oxidize and cause the voltage from the sensor to drop.

    Oxygen sensor are also used to check the efficiency of catalytic converters. They do this by checking before and after the converter and comparing the readings.

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  90. What is needed to test an automotive relay?

    Standard automotive relays can be tested with an ohmmeter. Many have a schematic printed on them and most use a standard pin pattern.

    For more information on checking fuses and relays, please see our Detailed Topic, How to check fuses and relays.


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  91. What is the average life of an automobile battery?

    The average life of an automobile battery across the US is about 38 months. This is considerably shorter than a few years ago. Increased demand on electrical systems is partially to blame for the decrease.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die. >.


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  92. What is the difference in a deep cycle and regular car battery?

    The difference is the way they are designed. Deep cycle batteries are designed to produce a steady current over a long period of time. A trolling motor in a boat would be a good candidate for a deep cycle battery. An automobile on the other hand requires a large amount of current to crank the engine, but only for a short period of time. The alternator supplies the steady demand for power, once the vehicle is running. For this reason, car batteries are designed to produce much larger amounts of current, but not for as long a period.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die.

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  93. What is the difference in a deep cycle battery and a regular car battery?

    The difference in a deep cycle and normal automobile battery is basically how much power they produce and for how long. Normal automobile batteries are designed to produce a large amount of amperage, for a short time. This is to produce the energy to crank the engine when cold.

    Deep cycle batteries are not designed to produce as much amperage, but they can provide power for longer periods of time. For instance a trolling motor in a boat, does not draw a large amount of current, but may be used for several hours. A deep cycle battery may not produce enough current to crank a car, and a car battery may not survive a long discharge period without recharge. Each type has a specific purpose.

    For even more information on batteries, please see our Detailed Topics article, Why Batteries Die.


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  94. What is the purpose of an alternator?

    The alternator converts mechanical energy of the engine into electrical energy. This energy is used to operate the various electrical devices in the automobile when the engine is running. The alternator also replaces energy used from the vehicle battery when the vehicle is not running. Without an alternator the vehicle battery will soon expend all of its energy and go dead.
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  95. When I turn my ignition switch to start I hear a loud click, but nothing else. Sometimes it will do this several times and then start. This is a General Motors vehicle.

    This problem is often caused by worn starter solenoid contacts. To isolate the problem an inductive amp meter should be connected to the positive cable and a volt meter to the starter terminal. With the symptom duplicated, see if amperage is very low and the voltage is normal. If so check voltage at the terminal that leads from the solenoid to the motor. If voltage is not present when the symptom occurs this is quite likely the problem. If milage is high, it may be most cost effective to replace the entire starter with the solenoid.

    For more information, please see our Detailed Topic, Why Does The Engine Not Crank?


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  96. When should I replace my vehicle battery?

    Many experts state the average life of a car battery is about 38 months. This will vary somewhat, but in our experience is about right. Weak batteries can damage the alternator, starter and cause all sorts of electrical problems. With the fairly low cost of a battery, relative to the service it provides, I feel changing it before failure is wise. I normally recommend replacing the battery around 36 months. This allows the client to have it done at their convenience, rather than as an emergency.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die.

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  97. Why is the starter on my new car much smaller than the one on my older car?

    In the early nineties, car makers started using permanent magnet, gear reduction starters. These are physically much smaller, lighter and have fewer parts. Our experience has been they work very well and last much longer than the much larger starters of the past.
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  98. Why would my vehicle battery overheat?

    In most cases overheating is caused by over charging. On older vehicles limiting the charge was a function of the voltage regulator. On newer vehicles, system voltage is controlled by the power control module (PCM.) Over charging a battering will drastically shorten the life and can be quite dangerous. A charging battery produces gasses which can be explosive. Best is to have the vehicle checked immediately.
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  99. Without test equipment, is there a way to determine the cause of a misfire on an old carburetor type engine?

    A good starting point in fixing a misfire is to determine if you have a single cylinder or multiple cylinder problem. Without other equipment, a good way to determine this is with a vacuum gauge. Attach the gauge and note the reading. Remove the spark plug wires, one at a time, with the engine running. The vacuum should drop about the same amount when any wire is removed.

    IF it does not drop on any one cylinder, that cylinder is where the misfire is occurring. Swap the spark plug and wire with one on a cylinder that is not misfiring. If the misfire moves, the plug or wire is bad. If not check the compression on the engine and see if it that cylinder is low. IF the compression is low, the problem is likely an internal engine problem.

    If all cylinders make about the same difference, when the plug wires are removed, the miss is likely affecting all cylinders equally. This could be the caused by the carburetor, a bad vacuum leak, mis-routed plug wires or other things that affect all the cylinders equally.


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  100. Would a bad brake caliper cause the ABS and Traction control light to come on?

    It is possible under extreme conditions, but not likely. The caliper would have to seize, stop or drastically overheat the brakes. If this occurred the cause would likely be fairly obvious.

    Far more likely is an electrical issue in the system, such as a failed sensor, brake control module, etc. A qualified technician with the proper tools should be able to isolate this problem fairly quickly.

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  101. Would a deep cycle battery last longer in a vehicle I do not drive often?

    It may not last as long as a standard battery. Deep cycle batteries produce current over longer periods, but also require longer recharge times. If the vehicle is not driven much this could cause it to die even sooner. A better plan might be to use a computer controlled auxiliary charger, designed for the purpose, or try to drive the vehicle more.

    For even more information on batteries, see our Detailed Topics article, Why Batteries Die.

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