Engine Control Module: Testing and Inspection

On-Board Diagnostic System Check (Using A Tech 1 Scan Tool):

On-Board Diagnostic Wiring Circuit:

The on-board diagnostic system check must be the starting point for any driveability complaint diagnosis. Before using this you should perform a careful visual/physical check of the PCM and engine grounds for being clean and tight.

The on-board diagnostic system check is an organized approach to identifying a problem created by an electronic engine control system malfunction because it directs the service technician to the next logical step in diagnosing the complaint.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. The MIL (Service Engine Soon) should be "ON" steady with the key "ON"/Engine "OFF."
2. This test ensures that the PCM recognizes the diagnostic request signal from the DLC and is controlling the MIL (Service Engine Soon) properly.
3. If an invalid DTC is displayed, the Tech 1, PCM or PROM can be at fault. "Flashing" the DTC by grounding DLC terminal "B" isolates the cause of the invalid DTC.