Retrieving Codes
- Perform diagnostic circuit check before diagnosing vehicle using self-diagnostic system. See appropriate DIAGNOSTIC CIRCUIT CHECK
chart under DIAGNOSTIC CODE CHARTS.
- Fault code(s) can be retrieved using a scan tester connected to the ALDL connector or by counting flashes of the CHECK ENGINE light after grounding the diagnostic request terminal in the duty coupler, located near battery. See Fig 1
.
- Turn ignition off. Using a jumper wire, jumper between duty coupler terminals No. 2 and 3. Turn ignition on and observe CHECK ENGINE light. Read fault codes. Proceed to appropriate charts under DIAGNOSTIC CODE CHARTS
to diagnose fault codes.
- If no fault codes are stored, CHECK ENGINE light will flash on and off rapidly until jumper wire is removed. Count the number of flashes and look for pauses in flashing to ensure no fault codes are overlooked. If fault codes are stored, code will flash 3 times starting with the lowest code.
Courtesy of GENERAL MOTORS CORP.