General Description

The Engine Control Module (ECM) processes the various input information. The ECM sends the necessary electrical responses to control fuel delivery.
The input information has an interrelation to more than one output. One failed input can affect more than one Systems operation.

Diagnostic System Check-Computers and Controls Systems
The Diagnostic System Check-Computers and Controls Systems is an organized approach to identify a problem caused by an electronic engine control system malfunction. This diagnostic check must be the starting point for any driveability complaint diagnosis. The diagnostic 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:
^ Complete the Diagnostic System Check-Computers and Controls Systems.
^ Confirm that the on-board diagnostics are functioning properly.
^ Confirm there are no 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.

Use only the parameters listed in the Engine Scan Tool Data 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 ECM 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 Symptoms-Computers and Controls Systems.