1. Turn the ignition switch ON but do not start the engine.
2. The "CHECK ENGINE" light come on indicating the bulb is working. If the light fails to come on, the bulb may be burned
out or there may be a problem in the Check Engine light circuit.
3. Locate the diagnostic connector for the computer. It is usually located under the instrument panel near the steering
column. Insert a jumper between the "TEST" and "GROUND" terminals.
CAUTION: Refer to a shop manual for the proper terminal locations. Jumping the wrong terminals may cause damage to the
4. The Check Engine should now flash. The first code should be a code 12 (Flash, Pause, Flash Flash). Code 12 will repeat
If any other trouble codes are in the computer's memory, they will be displayed in numerical order starting with the lowest
number, and repeat three times. The codes will continue to repeat as long as the test terminal remains grounded.
NOTE: BE SURE TO WRITE DOWN ANY CODES THAT ARE PRESENT
NOTE: GM may use the same code number for different faults on different models of vehicles. That's why some code
numbers list more than one possible cause.
5. To exit diagnostic mode, turn ignition switch off and remove the jumper.
HOW TO CLEAR TROUBLE CODES
Trouble codes on most older vehicles can be cleared by removing battery voltage from the computer for at least 10 seconds.
Make sure the ignition switch is OFF, then remove the computer fuse from the fuse panel. Disconnecting the battery will also
work, but doing so will also cause the loss of stored information and presets in other electronic accessories such as the
radio, climate control system, memory seats, etc. Disconnecting the battery can also cause the computer to forget long term
fuel calibration adjustments, and may affect the operation of an electronic transmission until the computer can "relearn" the
The preferred method of clearing trouble codes is to use a scan tool.
Wednesday, March 6th, 2019 AT 6:03 PM (Merged)