Trailer Brake Controls

DTC C056D or C056E

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC C056D 33
- ECU Hardware Performance Special Memory Failure

DTC C056D 34
- ECU Hardware Performance RAM Failure

DTC C056D 35
- ECU Hardware Performance ROM Failure

DTC C056D 36
- ECU Hardware Performance EEPROM Failure

DTC C056D 39
- ECU Hardware Performance Internal Electronic Failure

DTC C056E 41
- ECU Software Performance Operational Software/Calibration Set Not Programmed




Circuit/System Description

This diagnostic applies to internal microprocessor integrity conditions within the trailer brake control module (TBCM). This diagnostic also addresses if the TBCM is not programmed.


Conditions for Running the DTC


C056D 33, C056D 34, C056D 35, C056D 36 or C056D 39
* Ignition ON.
* Runs once an ignition cycle.



C056E 41
* Ignition ON, engine OFF.
* Runs continuously.



Conditions for Setting the DTC

C056D 33, C056D 34, C056D 35, C056D 36 or C056D 39

The TBCM detected a failure in its microprocessor.

C056E 41

The TBCM is not programmed.


Action Taken When the DTC Sets

* The trailer brake control will be disabled at the end of the current brake apply for the remainder of the ignition cycle.
* The driver information center (DIC) will display Service Trailer Brake System.



Conditions for Clearing the DTC

* The condition for the DTC is no longer present.
* The TBCM clears the history DTC when a current DTC is not detected in 40 consecutive drive cycles.



Reference Information
Schematic Reference

Trailer Brake Control Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Trailer Brake Controls Description and Operation (Trailer Brake Controls Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Verification

1. Verify that DTC C056E is not set.

• If the DTC is set, program the TBCM.

2. Verify that DTC C056D is not set.

• If the DTC is set, replace the TBCM.




Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.


Control Module References (Programming and Relearning) for TBCM replacement, setup, and programming