Diagnostic Circuit Check

Diagnostic circuit check is an organized approach in identifying a problem created by an electronic engine system malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing a complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent unnecessary replacement of good parts.

1. Checks Malfunction Indicator Light (MIL) operation with ignition switch in ON position.
2. Checks if PCM's normal diagnostic mode is operating.
3. Checks if PCM's test diagnostic mode is operating.
4. Checks if engine will start.
5. Checks for any codes that are stored in PCM's memory with engine running.
6. Checks for any codes that are stored in PCM's memory with engine off. If (after clearing codes and cranking engine) no codes except Code 42 are set and engine does not start, go to CHART A2-3 in BASIC TESTING article in this section.
7. Checks if Code 51 (Switch Condition Signal) is functioning.
8. Checks if code(s) are intermittent problems.

Fig 1: Diagnostic Circuit Check Schematic (LSi)

Fig 2: Diagnostic Circuit Check Flow Chart (1 Of 2) (LSi)

Fig 3: Diagnostic Circuit Check Flow Chart (2 Of 2) (LSi) Switch Condition Signal