GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC C0550 35: Electronic Control Unit (ECU) Performance ROM Failure

DTC C0550 39: Electronic Control Unit (ECU) Performance Internal Electronic Failure

Circuit/System Description

The rear differential clutch control module (CCM) detects an internal malfunction.

Conditions for Running the DTC

The ignition switch is in the ON position.

Conditions for Setting the DTC

An internal CCM malfunction exists.

Action Taken When the DTC Sets

One or more of the following actions may occur:

    • All Wheel Drive Off (AWD Disabled), DIC message
    • Service All Wheel Drive (Service AWD), DIC message

Conditions for Clearing the DTC

    • The condition for the DTC is no longer present.
    • The DTC is not detected in 40 consecutive drive cycles.

Reference Information

Schematic Reference

All-Wheel Drive Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

All-Wheel Drive Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Verify DTC C0550 is not current.

If DTC C0550 is current, replace the CCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for CCM replacement, setup, and programming