My check engine light keeps coming on at random every now and then. Only seems to happen after I've been on the highway for several minutes, and it comes and goes. Sometimes it happens, sometimes it doesn't. The car seems to be running fine.

Any ideas?

(By the way, I have a 1991 Pontiac Firebird Formula with the 305 V8 TPI)

 

FL,

Scan the ECM for error codes. I'm guessing you'll see either a '32' or '44'.


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.)

 

Actually before I read your reply I discovered how to do all of this and I tried it. I got a code 45. I think it's because my air filter is dirty as all heck. So I'm gonna either go ahead and drop in a K&N Filter or, hopefully, make an intake.