Repair Topics / Car Computer-1 / Car Computer-2 / Car Computer-3

• How do I retrieve trouble codes?
• Do I have a burned fuse connector?
• How does an engine computer work?
• Why does my engine run rough?
• Why does the engine stall after replacing the battery?
• Why does my engine idle high?
• Why does my engine stall at idle?
• Why won't my engine crank over?
• How does a MAF mass air flow sensor work?
• How to test an oxygen sensor
• Why does my engine hesitate?
• How to reprogram a key fob remote control
• How to test a fuel injector

MORE: Engine computer questions

Car Computer ECM Questions and Answers - This category contains featured questions as examples. They relate to most vehicles.

Answer: Code 225 knock sensor signal not detected would indicate the knock sensor is not functioning.  Replacing it should fix your problem.

Question: 1992 Dodge Caravan mileage: 32,000.  "Service Engine" light came on.  Using the "ignition switch off to on 3 times and count..." method, I determined the diagnostic codes to be "12" and "21".  I saw from the previously asked questions that "12" simply means I'm "ready to read the code".  Can you tell me what the "21" code references?  Thanks.

Answer: Code "21" indicates a failed oxygen sensor.

Question: 1987 Buick Century mileage: 88,000.  Car suddenly stalled and continues to do so.  The service engine soon light is now on.  I checked the code and got code 4,2...parts store won't even tell me what that indicates.  Said it could be lots of things.  Can you help?  I thought it could be the MAP sensor or the computer.

Answer: Code 42 has to do with the electronic spark timing circuit.   There are a number of things included in that starting with the knock sensor, the ignition coil, the pick-up coil and the ignition module.

Question: 1992 Ford E-150 Clubwagon mileage: 72,000.  Get a code 173 checked h.e.g.o.  It was, ok ran all other computer checks they were good, I can't find a vacuum leak.

Answer: Try replacing the Mass Air Flow and check for leaky fuel injectors.

Question: 1983 Olds Achieva 2.3 quad 4.  it is showing engine code 43. Could you tell me what that is?  It has a new engine with 0 miles

Answer: Code 43 is map signal, voltage low.  Check the catalytic converter to make sure it is not plugged as it may be causing your code 43.

Question: 1988 Mercury Tercer mileage: 105,000.  The car has a computer code of 41 for oxygen sensor running too lean, but the car runs very rich.  I have replaced the oxygen sensor but yet the code remains.  Do you have any idea what may cause this code to remain and not go away?  It is the only code I have in the computer so I tried several times to erase the memory on computer by pulling battery cables 10 minutes and even overnight.  I have also checked the wiring on the sensor.  What do you suggest?

Answer: Check for leaking fuel injector and excessive fuel pump pressure.

Question: 1998 Cadillac Coupe Deville V8 4.1l mileage: 94,023.  How do I activate the computer to give me fault codes?

Answer:  Push the off and the warmer buttons on the air conditioning controls at the same time.

Question: 1989: Pontiac Grand Prix mileage: 79,000.  My car is having problems idling, it won', It stalls.  The service engine soon light comes on.  I got the diagnostic code off the car, it flashed code 33.  I was wondering if you could give me a hint on what could be wrong.

Answer:  Code 33 is a map sensor problem.  Check the engine for vacuum leaks.  Check the exhaust for blockage (catalytic converter).  The map sensor may be faulty.

Question: 1984 Oldsmobile Alero mileage: 50,000.  I have a 94 Olds Cutlass Supreme with a 3.1 M engine code.  The check engine light comes on intermittently with a code 77 (#3 EGR solenoid).   The EGR has been changed and all connections checked. I don't see any carbon or anything which could have held it open. Is there anything I should look for?

Answer:  Check for exhaust gas and or a plugged exhaust passage to the EGR valve.  If the valve does not sense exhaust pressure, it will give you a code 77.

Question: 1988 Ford F250 mileage: 120,000.  Thanks for any help.  I will try to be specific.  I purchased the truck about a month ago.  The "check engine" light comes on after being driven for 5 or 10 miles from a cold start.  EEC-IV codes were checked: Key On Engine Off test gives a code of 11 (system pass).  Continuous code (stored memory) issues 41 (system indicates lean) and a 34 (EVP voltage above closed limit).  I have recently replaced the EGR valve, the EVP sensor, and the oxygen sensor in an effort to correct this problem with no success.  Sometime before that, the MAP sensor was replaced.  The condition of the spark plugs and the engine temperature gauge do not indicate that the mixture is lean, at least not severely.  I set the timing (SPOUT shorted) to 10 degrees BTDC.  Except for this warning light, the motor seems to be running pretty smooth.  It has an automatic transmission (no overdrive) and air conditioning.  Any help would be greatly appreciated.

Answer:    Check the fuel pump pressure and replace the fuel filter if not recently done.  Try injector cleaner if the problem persists replace your Mass Air Flow Sensor.   The fuel injectors may need to be replaced.

Question: 1994 Chevy s10, miles: 78,000. The truck was purchased for our son has new engine and new carburetor. The check engine light is on and the code reads 41 and 24 we know the speed sensor but what could the 41 be for it is not in the book? We had someone look at it and he mentioned distributor reference voltage and hall effect something called HEI. Make some suggestions please and if you're wondering I am not the one doing the work thank goodness.

Answer: Replacing the coil pack with a new unit will probably solve your problems.

Question: 2005 Ford Ranger, mileage: 39,800. The check engine light came on in the truck. I popped the hood, looked at it, and saw that this thing had come disconnected, which is located next to where you pour the oil in. (Sorry for my lousy description, I don't know what it is.) So, I reconnected it, but the check engine light remained on. I took it to the dealership today and they said the oxygen sensor had gone out, plus I needed to have the fuel injectors cleaned, desludged and replace the fuel filter. I went ahead with the oxygen sensor replacement, but have to wait on the rest because of the cost involved. I was wondering, if you fix whatever it is that makes the check engine light come on, will it automatically go off or does a mechanic have to flip a switch?

Answer: No the light does not automatically go off. Only the OBD II scanning system can reset the MIL (malfunction indicator light, more commonly known as check engine light.)

Question: 2004 Pontiac Aztec, mileage: 39,000. It has a habit of dying when she comes to a stop. It starts right back up and idles fine. I changed the fuel filter two months ago and it ran fine until a week ago. At the time I changed the filter I checked for codes and had none. Now I have a code 3. What that code is I'm not sure the engine is a muti-port fuel injected engine. This all happens when the car is fully warmed up. Any ideas?

Answer: Try servicing the fuel injection. Clean the carbon deposits from the throttle bore and idle passage. Replace the Mass Air Flow Sensor and the problem will be solved.

Question:   1999 Dodge Pickup, mileage: 57,000. The check engine light came on so I took the pickup to the dealer and they reset it. They said the purge control solenoid was the problem. The light came on again a few days later. Is there a way I can reset without taking back to a mechanic?

Answer:   It sounds like the dealer missed the problem. Return to the dealer and insist on fixing it right. Note: Only the OBD II scanner system can reset the MIL (check engine light).

Question: I have been to the shop twice for the check engine light coming on. $70 bucks a shot. Each time it was an O² sensor, first one before the catalectic converter then the one after went. Now the lights are on again. (1995 4.0 Ford Ranger extended cab.)

Answer:   Your truck's computer controlled engine management system will "light" the check engine light and store a fault code for the Oxygen sensor when there is a problem. This may occur if the fuel mixture is too lean or too rich and beyond the adjustment limits of the computer. For example, a vacuum leak or plugged fuel filter may cause a lean condition. Excess fuel pressure from a failed fuel pressure regulator would result in a rich condition. Check and correct any of these or similar problems, i.e. leaking intake manifold gaskets, severely plugged air filter, incorrect location of vacuum lines. The oxygen sensors may be okay.

Question: I have a 1998 Pontiac Transport Van with a 3.1 engine. I replaced a dead battery, and now need to know if there is any kind of special start-up procedure to follow to reset any computer components.

Answer: Yes, you must drive your car 40 miles to reset system monitors.

Question: I have a 1984 Cadillac coupe Deville, 4500 liter engine. I am using the onboard computer system, and getting error codes: 21, 26, 44, 52, & 60. If you can tell me what these error codes mean, or where I can find a manual telling me I would greatly appreciate it.

Answer: Error Codes:
               21 - Throttle position sensor on high voltage side.
               26 - Throttle position sensor shorted.
               44 - Lean exhaust indication.
               52 - ECM Memory reset in indicator
               60 - Transmission not in drive.

Question: I recently replaced the air intake on my car with a after market model, and during the installation, I started the car without the Mass Air Sensor wire installed. Now, my check engine soon light is on, and I was wondering if there is any way to reset this.

Answer: The malfunction indicator light cannot be reset without an OBD II scanner tool. Your local automobile mechanic should be able to reset.

MORE: Engine computer questions

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