Reading Trouble Codes
- Perform on-board diagnostic system check before diagnosing vehicle using self-diagnostic system. See appropriate ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK chart under DIAGNOSTIC CODE CHARTS.
- Fault code(s) can be retrieved using a scan tester connected to Data Link Connector (DLC) or by counting flashes of Malfunction Indicator Light (MIL) after grounding the diagnostic request terminal in the duty check data link connector, located near battery. See Fig 1.
- Turn ignition off. Using a jumper wire, connect between duty check data link connector terminals No. 2 and 3 (TBI - Federal) or No. 2 and 4 (MFI - Calif. and New York). Turn ignition on and observe MIL to read fault codes. If fault codes are stored, code will flash 3 times starting with the lowest code. Proceed to appropriate charts under DIAGNOSTIC CODE CHARTS to diagnose fault codes. See SELF-DIAGNOSTICS DIRECTORY table.
- If no fault codes are stored, MIL will flash Code 12, indicating ECM diagnostic system is operating.
Courtesy of GENERAL MOTORS CORP.