Repair Topics / Check Engine Light-1 / Check Engine Light-2 / Check Engine Light-3 / Check Engine Light-4

• Why is my service engine soon light on?
• How to use a code reader
• How to tune up your engine
• Why does my engine stall?
• Why is my engine running rough?
• Why wont my engine crank over?
• Why does my engine stall at idle?
• How does a MAF mass air flow sensor work?
• How to test an oxygen sensor

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Question: 1999 Olds LSS 3.8 mileage: 51,000. My Olds LSS cuts out between 40 - 55 mph, especially when the A/C is on and on an incline. It feels as if it a fuel line plug, or severe loss of spark when it occurs. It's had (at least) the following performed: new plugs, wires, fuel filter, injectors cleaned, computer reset. The problem is hardly noticeable without the A/C on, but pronounced with it.

Answer: You mentioned having the computer reset, we assume to clear fault codes. The codes will tell you what is malfunctioning in your can. You need to have the fault code read to determine what the problem is.

Question: 1999 Chevy z-28 v8 mileage: 37,000. I ran a diagnostic test and it read: "Code 0174" from the Actron II tester OBD II (system to lean -Bank 2) what is the remedy?

Answer: Several things can cause a lean condition: an Oxygen sensor, a partially plugged fuel injector, a partially plugged fuel filter, and or a faulty fuel pump.

Answer: A boost pressure that is too high causes a turbo boost problem. Check the waste gate as it may be hanging up causing the over boost.

Question: 1999 Mercury Grand Marquis 4.6L mileage: 142,000. Howdy, Every several hundred miles or so (between code clearing), the check engine light will come on. The codes are 0171 and 0174 indicating a lean condition. Gas mileage is also down about 10%. I have replaced the fuel filter, fuel pressure regulator (fuel pressure is 31 psi with vacuum and 42 psi without) and EGR valve. I have also tuned the car, replacing plugs, plug wires and air filter. Any ideas as to what is triggering the codes?

Answer: Check for vacuum leaks if ok, try replace the oxygen sensors.

Question: 1995 Dodge Caravan " mileage: 210,000 km. Bonjour Bob, Allo Ken, I've already checked the Q & A archives and I think I know where this problem is leading, probably big $$$, but I'll ask anyway. 5 months ago the check engine light was giving me a ' 46' fault code. The battery was being overcharged and was replaced. That seemed to have fixed the problem except that the oil pressure gauge wasn't working properly. It would register some pressure but always on the lower side of the gauge. I just now, replaced the oil pressure switch (while the engine was cold) and took it out for a quick test and everything seemed to be working fine until the engine came up to temperature. The battery charge gauge went way up and the battery boiled over. The oil pressure gauge is still reading low pressure (with the new switch). I let the engine cool down and checked out the battery and topped it up (unsealed battery). Now, although the battery is not being overcharged (the charge gauge is slightly right of center) I still get the "check engine" light, and a '46'-fault code. Is it the computer giving out the wrong signals causing the alternator to overcharge the battery? Can something as simple as a faulty oil pressure switch trigger this series of events or does one thing have nothing to do with the other. Thanks for your time and consideration. Dan - Montreal, Canada

Answer: The computer has a voltage regulator built into it. If it malfunctions, it will cause the alternator to overcharge the battery. Check the ground wires for the computer as a bad ground may also be causing your problem.

Question: 1996 Dodge B2500 Van V6 mileage: 86,000. Check engine light came on. Pulled out both oxygen sensors. Each was sprayed with PB blaster (cleaner). Replaced sensors and now engine won't start. Is the cleaner the culprit?

Answer: Spraying cleaner on the oxygen sensors is not a good idea. They have probably shorted out keeping your van from starting. It may start if you disconnect the sensors. If it does start, replace both sensors.

Question: 1996 Acura Legend V6 mileage: 95,000. This is a car I am looking to buy. It is in excellent condition, just inspected, passed emissions, no engine or transmission noises. But, a PGM-FI light comes on after a couple of minutes. There seems to be no engine performance changes before or after the light comes on. Any ideas on what it means or how to check what is causing it?

Answer: The PGM-FI light is another word for "check engine light." The "check engine" light will "light" when there is a malfunction in the engine management system. The fault code is then stored in the computer. The computer must be scanned to retrieve these stored faults to pinpoint the malfunctioning component. Because the check engine light indicates something is wrong, a trip to you neighborhood automobile service center sooner rather than later is recommended.

Answer: To answer your first question, yes, the problem can be determined even if the service light is out. When the engine service light comes on, it is because a fault code is being stored in the computer. This information is held in the computer until it is scanned and cleared. You may or may not have noticed any poor performance as a result of a malfunctioning EGR valve. It would depend on the degree of failure.

Question: 1993 Pontiac Grand Am 2.3 quad 4 mileage: 78,381. My 94 Grand Am service engine soon light keeps lighting up. I tried retrieving the error codes from the computer by jumping the a & b terminals on the computer. I did not receive any codes (flashes). I had been having problems with stumbling during acceleration and occasional stalling. I have replaced the fuel filter, spark plugs, vacuum lines, M.A.P. sensor, catalytic converter, and oxygen sensor. The car is running better, however the light still comes on after running for a while. I have reset the computer. But the light still lights up. The fuel injectors sound to be working using a screwdriver I here them clicking. Do you have any insight?

Answer: Jumping the A and B terminals on the computer may or may not give you the stored fault codes. The proper way is to scan it with an OBDII scanning tool. This will pinpoint malfunctioning components.

Answer: It is possible that the MAP (manifold absolute pressure) was affected by the altitude.  They only way to tell for sure is to have the computer reset and this can only be down with the proper equipment.

Question: 1997 Ford Mustang mileage: 96,000.  Engine is idling at 2000-3000 rpm.  Hoping this was just an intermittent problem; I have attempted to reset the computer by disconnecting the battery for about 10 minutes.  After driving a short distance, the idle will sometimes correct itself, at other times the "Check Engine" light will come on.  The car runs fine other than the fast idle.  This problem came on suddenly shortly after having the engine cleaned.   Mere coincidence or could it be related?

Answer: 1994 and later model cars will not clear the computer by disconnecting the battery.  Cleaning the engine may be the cause of your problem.  All the sensors and controllers are very sensitive to moisture and corroded connections, which will give faulty readings to the computer.  Now that your car has dried out, scanning the computer for fault codes which should pinpoint your problem.

Answer: You might want to do a fuel pump pressure check and check the fuel pressure regulator.  The “check engine” light will “light” when there is a malfunction in the engine management system.  The fault code is then stored in the computer.  The computer must be scanned to retrieve these stored faults to pinpoint the malfunctioning component.   If you are sure there are no codes stored in the computer, it is possible that you have a faulty computer.

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• How to Scan for a Check Engine Light
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