GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 STS 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC C056D

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 provide an overview of each diagnostic category.

DTC Descriptor

DTC C056D 39: ECU Hardware Performance Internal Electronic Failure

Circuit/System Description

The power steering control module (PSCM) continuously monitors the internal circuitry within the module.

Conditions for Running the DTC

Ignition ON.

Conditions for Setting the DTC

The PSCM detects an internal malfunction within the module.

Action Taken When the DTC Sets
    • Active Steering is disabled.
    • SERVICE STEERING SYS and/or STABILITY SECURE MODE is displayed on the DIC.

Conditions for Clearing the DTC
    • A current DTC will clear on the next malfunction free ignition cycle.
    • A history DTC will clear after 100 consecutive malfunction free ignition cycles.

Reference Information

Schematic Reference

Power Steering Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Active Front Steering 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 Testing
  1. Ignition OFF, disconnect the X2 harness connector at the PSCM.
  2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal 1 and ground.
    3. ⇒If greater than specified value, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 6 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. Ignition OFF, reconnect the X2 harness connector. Disconnect the X3 harness connector at the PSCM.
  5. Ignition OFF, test for less than 5 ohms between the ground circuit terminal 3 and ground.
    6. ⇒If greater than specified value, test the ground circuit for an open/high resistance.
  6. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 and ground.
    7. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  7. Test for B+ on the control circuit terminal 10.
    8. ⇒I less than specified value, test the control circuit for an short to ground or an open/high resistance.
  8. Ignition OFF, reconnect the X3 harness connector. Disconnect the X1 harness connector at the PSCM.
  9. Test for less than 5 ohms between the signal circuit terminal 7 and the signal circuit terminal 8.
    10. ⇒If greater than specified value, test both signal circuits for an open/high resistance. If the circuits test normal, test or replace the upper intermediate steering shaft.
  10. Test for less than 5 ohms between the signal circuit terminal 7 and the signal circuit terminal 14.
    11. ⇒If greater than specified value, test both signal circuits for an open/high resistance. If the circuits test normal, test or replace the upper intermediate steering shaft.
  11. Test for less than 5 ohms between the signal circuit terminal 8 and the signal circuit terminal 14.
    12. ⇒If greater than specified value, test both signal circuits for an open/high resistance. If the circuits test normal, test or replace the upper intermediate steering shaft.
  12. If all circuits test normal, replace the PSCM. If the DTC resets, replace the upper intermediate steering shaft.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for PSCM replacement, setup, and programming