I'm not sure if this an engine question but I need help. The last few days my service engine light has been coming on. It only comes on in the evening though. When I go to work in the morning it has never come on, but when I go home in the evening it comes on after about four miles or so. I checked my oil, coolant, and plug wires and everything is fine. My car isnt overheating at all although it does run 5-10 degrees hotter in the evening. Even then its only at 195-200 degrees. A couple of times I shut the car off while the light was on and then turnes it back on right away and the light doesn't come back on, at least not within the couple minutes I let it run. I have no idea what the problem could be. Any comments would be helpful.

 

Usually, when the check enging light is coming on, it indicated that a sensor has gone bad. Check the codes to see which code yo get, and go from there.

 

Yes. Scan for error codes. It's really very easy to do.

First, you'll need to acquire a GM OBD I ECM Diagnostic Trouble Code Retrieval Tool (commonly known as a paper clip to TGO members). You'll also need to have a Diagnostic Trouble Code recorder. I use a 3¼ x 5 ruled index card and genuine cedar #2 pencil, but I suppose any note pad and writing instrument will work for a first-timer.

With the engine and ignition turned off, locate the ALDL connector under the dash, just to the right of the steering wheel in the driver's foot well area. There should be a small rectangular cover over the access hole in the lower dash trim.



Insert a tool as described above (paper clip) into the 'A' and 'B' terminals on the ALDL connector:



WITHOUT STARTING the engine, turn the ignition to the "RUN" position. Watch the Malfunction Indicator Lamp (MIL) and it will begin to flash. This is also commonly called the "Service Engine Soon" or "SES" lamp. The first code will flash three times, and will usually be a code '12'. This is encoded by one flash of the lamp, a brief pause, then two successive flashes of the lamp. Each code will repeat three times, so you should see a "Code 12" flash three times. Any other error codes will follow in numerical order, and each code should flash three times. After all codes have been displayed three times, the "Code 12" will again flash three times, then all other codes will follow as described earlier. This cycle will continue until the jumper is removed or the ignition is turned off.

After you have made a note of all error codes, turn off the ignition and remove the jumper immediately. If you forget to remove the jumper and attempt to start the engine with it in place, you could damage the ECM. For this reason you should remove it immediately.

Once you have a note of all error codes, check this file for the decoding:

GM Error Codes.pdf.

You'll need Adobe Acrobat Reader to open/print the file. (See link below.)