AGCO Automotive Vehicle Questions Page

 Vehicle Questions
Warning Lights and Electrical Systems
QUESTIONS
  1. 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?
  2. 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?
  3. Can you help, I have an old Suburban and the left turn signal flashes very fast, while the right flashes at normal speed?
  4. 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?
  5. My battery cables are corroded, should I replace the ends with bolt on terminals?
  6. I have an older Chevy pick up that runs fine, but my air bag light stays on. What does this mean?
  7. 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?
  8. 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?
  9. 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?
  10. 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?
  11. I have seen code readers advertised in several magazines. Can I save money by buying one of these and fixing my own vehicles?
  12. 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?
  13. 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.
  14. Does the check Engine light come on when my vehicle needs routine maintenance?
  15. 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.
  16. 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?
  17. 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.
  18. 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.
  19. 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?
  20. 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?
  21. An oxygen sensor caused the check engine light to come on in my vehicle. What is the purpose of an oxygen sensor?
  22. What does the term OBDII mean in reference to my vehicle?
  23. My check engine light came on and after repair the invoice listed code P0304. Does this code have a specific meaning?
  24. What does the light labeled “Check Engine” indicate?
  25. I am taking a long trip, can an alternator be tested to determine if it might fail?
  26. What do OBDII codes actually mean?
  27. 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.
  28. I have a light that says SIR, what does it mean?
  29. Is there a way to disable the check engine light on my Suburban?
  30. 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.
  31. My vehicle was recently wrecked in the front but the air bag did not deploy. Is this a defect?
  32. 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?
  33. Does being low on oil make a check engine light come on?
  34. 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.
  35. My vehicle failed the State emissions inspection and I was told it was because my cigarette lighter did not work. How can that be?
  36. The check engine light was on in my car. A parts store cleared the codes but my car still failed inspection.
  37. 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.
  38. Recently my vehicle air conditioner was repaired. Shortly after picking the vehicle up, the check engine light came on. Could this be a coincidence?
  39. My ABS brake light is on but there are no symptoms.
  40. 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?
  41. 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?
  42. Does the check engine light come on for automatic transmission problems?
  43. What does a flashing over-drive light indicate?
  44. The anti lock brake light is on in my vehicle, but no codes show with a code reader.
  45. I have several weird electrical problems with my vehicle. Where is the best place to start looking?
  46. Several alternators have been replaced on my vehicle. Is this just poor quality parts?
  47. Can corroded battery cables cause an engine to run rough?
  48. What is a starter solenoid and how does it work?
  49. What is an automotive O2 sensor used for?
  50. 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?
  51. What is the difference in a deep cycle and regular car battery?
  52. Would a deep cycle battery last longer in a vehicle I do not drive often?
  53. When should I replace my vehicle battery?
  54. How can I be sure I get the correct replacement vehicle battery?
  55. Can an alternator bearing be replaced?
  56. Can water short out an alternator?
  57. How can I tell how many amp alternator I have with out taking it off?
  58. Why would my vehicle battery overheat?
  59. How does the check fuel cap light work?
  60. After doing some under-dash work, my SIR light is on. How can I reset the light?
  61. My brake lights are not working. How can I test for the brake light switch?
  62. 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?
  63. I put a locking gas cap on my car and now the check engine light comes on?
  64. What does the check suspension message on my Lincoln indicate?
  65. Why is the starter on my new car much smaller than the one on my older car?
  66. How much of a drain is the alternator on the engine?
  67. How much of a drain is the alternator on the engine?
  68. What are the symptoms of a bad alternator?
  69. 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?
  70. 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?
  71. Would a bad brake caliper cause the ABS and Traction control light to come on?
  72. I have an odor, almost like rotten eggs coming from under the hood of my vehicle.
ANSWERS
  1. After doing some under-dash work, my SIR light is on. How can I reset the light?

    The SIR or air bag system is self testing and resetting. If the light is on, there is still a fault in the system. Check all connections to the air bag system. When the problem is corrected, cycle the ignition switch. The light will go out, after a short self test period.
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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 to politely inform the shop that there is a problem and ask them to check it for you. If you do not agree with their explanation, a second opinion 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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  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 different types and serve different functions. Vehicles may have as few as one or several. The basic function is to tell the power control module (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 used economy will suffer and components can be damaged. Too little will also cause running problems and damage to components. Improper mixture can also result in damage to the catalytic converter(s) which can be extremely expensive.

    A different type of oxygen sensor is also used to monitor the function of the catalytic converter and test it’s efficiency.
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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 cost. It requires significantly more time to replace the bearing than the whole unit. Since time is money, 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 and 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 may not 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 on this vehicle often indicates one of the turn signal lamps is not operating. First check all of 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. Many technicians suggest to prevent future occurrences, replace the bulbs with LED type of the same number. The LED bulbs draw lower amperage and last much longer.
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  8. Does being low on oil make a check engine light come on?

    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 for the driver that 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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  9. Does the check engine light come on for automatic transmission problems?

    Most vehicles built after 1996 do have sensors in the automatic transmission that allow the computer to monitor operation. A few of the 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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  10. 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. It’s purpose is to monitor the computer operating system and sensors that run a vehicle. When it comes on a malfunction has occurred and should be addressed by a professional technician 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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  11. 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 are inside the starter and can be replaced without replacing the entire starter. A diagnostic test would be to connect a volt meter between the battery terminal on the starter and ground. If there is 12 volts present, as the key is held in start position and the click occurs, the contacts are likely the cause.
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  12. 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 insure the battery will fit. The group number does NOT take quality of the product into account however. When choosing a replacement battery, the advise of a trusted professional can be quite valuable.
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  13. 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 data base 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.
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  14. 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 test 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 evap system should be checked.

    Please see our Detailed Topic Evaporative Emissions Systems and Fuel Caps for more information.
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  15. 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 full charge. Because of this high power consumption and the heat generated, modern vehicles regulate output to just above what is needed.
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  16. 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 full charge. Because of this high power consumption and the heat generated, modern vehicles regulate output to just above what is needed.
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  17. 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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  18. 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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  19. 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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  20. 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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  21. 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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  22. 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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  23. 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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  24. 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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  25. 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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  26. 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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  27. 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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  28. 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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  29. 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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  30. 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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  31. 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.
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  32. 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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  33. 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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  34. 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 fourth 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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  35. 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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  36. 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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  37. 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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  38. 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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  39. 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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  40. 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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  41. 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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  42. 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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  43. 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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  44. 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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  45. 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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  46. 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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  47. 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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  48. 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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  49. 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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  50. 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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  51. 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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  52. 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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  53. 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.

    See our Detailed Topic article GM Dash Gauge Failure for far more details.
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  54. 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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  55. 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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  56. 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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  57. 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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  58. 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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  59. 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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  60. 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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  61. 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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  62. 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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  63. 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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  64. 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.
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  65. 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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  66. 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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  67. 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.
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  68. 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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  69. 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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  70. 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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  71. 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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  72. 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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