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 ECM's normal diagnostic mode is operating.
3. Checks if ECM's test diagnostic mode is operating.
4. Checks if engine will start.
5. Checks for any codes that are stored in ECM's memory with engine running.
6. Checks for any codes that are stored in ECM's memory with engine off. If no codes are stored after cranking and engine will not start, go to CHART A1-3 IN BASIC TESTING article.
7. Checks if Code 51 (Switch Condition Signal) is functioning.
8. This step checks if code(s) are intermittent problems.

Fig 1: Diagnostic Circuit Check Schematic (Except LSi)

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

Fig 3: Diagnostic Circuit Check Flow Chart (2 Of 2) (Except LSi)