GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

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

DTC Descriptor

DTC C1550 36: ECU Failure EEPROM failure

DTC C1550 37: ECU Failure watchdog/safety failure

DTC C1550 38: ECU Failure supervision software failure

DTC C1550 39: ECU Failure internal electronic failure

DTC C1550 3A: ECU Failure incorrect component installed

Circuit/System Description

Conditions for Running the DTC

DTC C1550 38

Engine starting

DTC C1550 36

Engine running

DTC C1550 39

    â€¢ Engine starting
    â€¢ Engine running

Conditions for Setting the DTC

DTC C1550 36, 38, 39

    â€¢  Control unit software/hardware failure.
    â€¢ Above condition must be fulfilled for at least 0 seconds.

Action Taken When the DTC Sets

DTC C1550 36

No steering boost function

DTC C1550 38

The system function is not affected.

DTC C1550 39

    â€¢  The steering boost is switched off.
    â€¢  The system function is not affected.

Conditions for Clearing the DTC

A history DTC will clear after 60 consecutive malfunction-free ignition cycles.

Reference Information

Schematic Reference

Power Steering Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Power Steering System Description and Operation

Electrical Information Reference

    â€¢  Circuit Testing
    â€¢  Connector Repairs
    â€¢  Testing for Intermittent Conditions and Poor Connections
    â€¢  Wiring Repairs

Circuit/System Verification

  1. Verify that DTC C1550 is not set.
  2. ⇒ If the DTC is set, reprogram the PSCM. If the DTC resets, replace the PSCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.