Diagnostic Procedure

The Diagnostic System Check will provide the following information:

• The identification of the control module(s) which command the system.
• The ability of the control module(s) to communicate through the serial data circuit.
• The identification of any stored Diagnostic Trouble Codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

1. Install a scan tool. Does the scan tool turn ON? If yes, go to next step. If no, see SCAN TOOL DOES NOT POWER UP in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
2. Turn ON the ignition, with the engine OFF. Attempt to establish communication with the instrument cluster and ECM. Does the scan tool communicate with the ECM? If yes, go to next step. If no, see SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
3. Select the ENGINE CONTROL MODULE DISPLAY DTCS function on the scan tool. Does the scan tool display any DTCs? If yes, go to next step. If no, see COOLING SYSTEM TROUBLE SHOOTING under ENGINE MECHANICAL in TROUBLE SHOOTING - BASIC PROCEDURES article in GENERAL INFORMATION.
4. Does the scan tool display DTCs which begin with a "U"? If yes, see appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT for diagnosis. If no, see DIAGNOSTIC TROUBLE CODE DEFINITIONS .