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 Descriptors

DTC C1255 00: Electronic Control Unit (ECU) Performance

DTC C1256 00: Program Read Only Memory (ROM) Checksum Error

Circuit/System Description

The engine control module (ECM) receives a serial data message from the electronic brake control module (EBCM) is detecting an internal malfunction.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

An internal EBCM malfunction exists.

Action Taken When the DTC Sets

The MIL indicators turns ON.

Conditions for Clearing the DTC

    • The condition for the DTC is no longer present.
    • The ECM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Reference Information

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

ABS 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 that DTC C0550 is not set in the EBCM.

If DTC is set, refer to DTC C0550.