Note: The procedure provided below is applicable for most GM models.
1. Locate the diagnostic connector. It is usually located under the driver side dashboard, near the fuse box.
2. Turn the key to the "On" position, but do not start the engine.
3. Find the ALDL port, a white or gray 12-pin connector.
4. If you do not see a check engine light on the dashboard, use a jumper wire to connect the "A" and "B" terminals of the ALDL port.
5. Turn the key to the "On" position again.
6. If the check engine light comes on, the diagnostic system is working correctly.
7. If the check engine light does not come on, there may be a problem with the diagnostic system.
If the check engine light is on and does not go off, it means there is a trouble code stored in the computer. To retrieve the trouble code, follow the steps below:
1. Connect a scan tool to the ALDL port.
2. Turn the key to the "On" position.
3. Follow the prompts on the scan tool to select the option to retrieve trouble codes.
4. The scan tool will display any stored trouble codes.
5. Record the trouble codes and look them up in a GM OBD1 Code Reader to find out what they mean.
