WOW! I have this problem posted all over the internet in many forums and you are the first person to say the computer is not working. I keep thinking the computer must be fried and everyone keeps saying "no, that can't be it". All fuses have been checked. Even the ones that have nothing to do with it. I'm on my second multi-meter from checking and rechecking wires etc. I swapped the relays around and even tried some I had from past vehicle (I'm a bit of a hoarder like that). Here is what I recently posted on another forum thinking the pcm (computer) is totally dead:
I opened the PCM but saw no physical signs of damage. There are other reasons why I am beginning to suspect the PCM though.
1. For the past year the oil light will come on at idle once the car is warm. I know there are many things that can cause this. The sending unit was replaced and it still did it. Using a pressure guage it tested in the normal. Sometimes it would never happen at all but in the past few months it always did it. Still shows normal under guage tool.
2. Over the past year the car will be at idle and start to shake and sputter and sometimes die for no reason and no check engine light or pending codes.
3. The theft system light came on about 3 weeks ago after the car seemed to lose power for a brief moment. After I turned the car off and restarted it was gone. Since that time the theft system light has came on during "lamp test" when the ignition is turned on but went off with the rest of the lights when the car was started. I do not recall the theft light ever illuminating during "lamp test" before this time. (I may be wrong and just never noticed).
4. Over the past 2 weeks. The car will lose power very briefly even when at 35 to 65mph. Like a missfire but the gages all drop slightly then shoot right back up. Still no codes. (In my experience this type of behavior will set a code in most OBDII cars). It has done this 4 or 5 different times over the past week.
5. I can confirm that the PCM for several weeks and possibly even months (dating back to cold weather) will not send a signal to start the fan. (Mechanic shop confirmed this). I had to run the AC for the fan to come on. This was confirmed on a cool night a couple weeks ago when I turned the AC off and the car ran hot waiting on a train to pass.
6. The old fan motor which was replaced the night prior to this mess had a short in it. Once the car ran hot and the fan was identified as being weak I could push down on the connector and it would speed up but not to full power and if I let off it would die or reduce fan speed. If it didn't come on at all I could hit it on the back and it would start. This along with the fact that the fan has not been getting a signal from the PCM to turn on make me think that maybe a short in the fan somehow damaged the PCM. The new fan ran perfectly without issue but still would not be turned on by the PCM. (And yes all other related items were checked. I even replaced the temperature sending unit 2 times and all relays fuses etc are good).
7. My father in law next door likes to use my car to jump start his riding mower which doesn't even have a battery in it. I told him to stop last summer after he melted my jumper cables but I think he waits till I'm not home and does it anyways.
With all this in mind can anyone think of anything other than the PCM that would cause my symptoms? Some of the stuff above may have nothing to do with the PCM. Can the short in the fan motor even have any effect on the PCM?
I have even tried to get people to remove their pcms from 97 -99 Cavaliers/Sunfires to see if the symptoms match up. No takers though. Would a bad instrument cluster cause this? The PCM and cluster are the only 2 things I can think of.
Thursday, August 4th, 2011 AT 4:16 AM