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 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

    • Engine starting
    • Engine running

Conditions for Setting the DTC

DTC C1550 36, 38, 39

    •  Control unit software/hardware failure.
    • 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

    •  The steering boost is switched off.
    •  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

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