Engine Control Module: Testing and Inspection

The On-Board Diagnostic (OBD) System Check is an organized approach to identify a problem caused by an electronic engine control system malfunction. The OBD must be the starting point for any driveability complaint diagnosis. The OBD directs the technician to the next logical step in diagnosing the complaint. Use the Engine Scan Tool Data Definitions list for a comparison after fulfilling the following items:
^ Completes the OBD System Check
^ The on-board diagnostics are functioning properly
^ Displays no diagnostic trouble codes

Reading and Clearing Diagnostic Trouble Codes

The Engine Scan Tool Definitions are an average of display values recorded from normal operating vehicles. The Definitions intend to represent what a normal functioning system should display.

IMPORTANT: Do not use a scan tool that displays faulty data. Report the problem to the manufacturer. Using a malfunctioning scan tool can result in misdiagnosis and unnecessary parts replacement.

Symptom Related Diagnostic Procedures

Use only the parameters listed in the Engine Scan Tool Definitions for diagnosis. When a scan tool reads other parameters, General Motors recommends not using the values for use in diagnosis.

For more description on the values and the use of the scan tool to diagnose the PCM inputs, refer to the applicable diagnostic file.

When all the values are within the range illustrated in the Engine Scan Tool Data Definitions, refer to Driveability Symptoms.

Symptom Related Diagnostic Procedures