Can you get a service engine code on a 91 corsica without a diagnostic computer?

Answer 1

Yes. On the underside of the dash panel, approximately above your left knee, is a black female connector plug. This is called the ALDL plug, and is where techs plug in their diagnostic instruments. But GM was kind to us poor-boys, and built in a method to extract the basic fault codes that the car's engine computer (ECM) sets. Here's the procedure:

You want to jumper pins A and B. That should be the two upper right pins as you look at the plug.

1. With power off, jumper pin A to pin B (A bent metal paper clip works fine.)

2. Turn the ignition to ON but DO NOT start the vehicle.

3. The Service Engine Soon (SES) light should flash code 12 (1 flash, pause, 2 quick flashes)

4. After a longer pause, code 12 should repeat two more times.

5. If there are any codes stored in the ECM they will follow Code 12.

5a. Codes are two digit, and are indicated by flashes of the SES light. For instance three blinks--pause--four blinks = code 34. One blink--pause--six blinks=Code 16. If multiple codes are set, they will flash lower numbers first, and repeat the sequence of numbers several times. If you Google "GM OBD 1 Codes" there are many sites with lists of what the codes mean. GM says you should address the problems indicated by the lower code numbers first.

6. If no other codes have been stored then Code 12 will continue to repeat until the jumper is disconnected.

7. Incidentally, this diagonostic should also cause the cooling fan to run, testing the wiring, the fan relay, and the cooling fan (radiator) motor.

Good Luck !