Always Start Electrical Or Electronic Diagnosis Here

1. SERVICE ENGINE SOON telltale light at key ON confirms battery, ignition, and ground integrity to ECM and also verifies Ignition 1 power feed to IPC.
2. IPC odometer is primary display device for diagnosis and must be functional in order to use self-diagnostic system.
3. ECCP serves as access for onboard diagnosis and must be functional in order to use self-diagnostic system. A display other than standard temperature indicates fault that must be corrected before diagnostics can be entered.
4. After entering diagnostics, record all displayed trouble codes and note if they display as CURRENT or HISTORY. Codes displayed as current may be diagnosed using the procedures outlined in this article, but those codes displayed as HISTORY are not presently falling and may require visual inspection of circuitry to isolate.
5. Failure of SERVICE ENGINE SOON light to go out in the expected time period indicates ECM problem.
6. If no fault is found and driveability problems exist, see appropriate TESTS W/O CODES article in the ENGINE PERFORMANCE section for diagnosis by symptom.

Fig 1: Self-Diagnostic System Troubleshooting Chart (Reatta & Riviera)

Courtesy of GENERAL MOTORS CORP.