Engine Control Module: Testing and Inspection

Diagnostic Circuit:

Circuit Description:
The Diagnostic Circuit 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 diagnostic circuit 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.

Diagnostic Circuit Check:

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

1. The "Service Engine Soon" light should be "ON" steady with the key "ON"/Engine "OFF."

2. This test ensures that the PCM recognizes the diagnostic request signal from the ALDL and is controlling the "Service Engine Soon" light properly.

3. If an invalid code is displayed, the Tech 1, PCM or MEM-CAL can be at fault. "Flashing" the code by grounding ALDL terminal "B" isolates the cause of the invalid code.