Diagnostic Circuit Check

Diagnostic Circuit Check:

SYSTEM CHECK

Since this is the starting point for the diagnostic procedures or finding the cause of an emissions test failure, always begin here.

The system check is performed through the twelve terminal assembly line diagnostic link (ALDL) connector under the instrument panel in the passenger compartment.

The Computer Command Control System Check is a procedure that determines the following:

1. Bulb Check - to check SES light circuit and that the ECM can complete the circuit.

2. Diagnostic Mode - this indicates if the diagnostic code system is working.

3. "Scan" Data - this determines if the ECM is supplying input and output visual data.

4. Engine Start - this step is done after it has been determined that the ECM will display codes and data.

5. Other Codes - Proceed to applicable chart if a code is displayed. Scanning the data for typical value may indicate a problem area if they are incorrect. If all systems appear to be functioning, see Diagnosis by Symptoms - No Trouble Codes Stored.

The system check starts with a bulb check. If there is no "Service Engine Soon" light, refer to CHART A-1.