SELF-DIAGNOSTICS
The PCM constantly monitors all electrical circuits. If the PCM detects circuit problem(s) or out-of-range sensor(s), a trouble code(s) will be recorded in computer memory. If problem continues for a preset time, the TRANS or SERVICE ENGINE SOON light will glow.
If the TRANS or SERVICE ENGINE SOON light is always on, trouble code(s) is currently being detected. If the TRANS or SERVICE ENGINE SOON light is off, but PCM has detected a circuit or sensor problem, trouble code(s) will be stored in computer memory.
Stored trouble codes may be retrieved from PCM memory using Scan tester or TRANS or SERVICE ENGINE SOON light. See appropriate RETRIEVING CODES procedure under ELECTRONIC SELF-DIAGNOSTICS.
Note. For complete PCM testing and diagnosis, see appropriate TESTS W/CODES article in ENGINE PERFORMANCE section.