Antilock Brake System

DTC C0242 or P0856

Diagnostic Instructions

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

DTC Descriptors
DTC C0242 00
- ECM Indicated TCS Malfunction

DTC C0242 71
- ECM Indicated TCS Malfunction, Invalid Serial Data

DTC C0242 75
- ECM Indicated TCS Malfunction, Signal Above Allowable Range

DTC P0856
- Traction Control Torque Request Circuit

Circuit/System Description

The electronic brake control module (EBCM) and the engine control module (ECM) simultaneously control the traction control. The EBCM sends a serial data message to the ECM requesting torque reduction. When certain ECM DTCs are set, the ECM will not be able to perform the torque reduction for traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

Conditions for Running the DTC

* Ignition ON.
* Ignition voltage is greater than 10 volts.

Conditions for Setting the DTC

The ECM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The ECM will typically set other DTCs and the EBCM will set DTC C0242.

Actions Taken when the DTC Sets

* The EBCM disables the antilock brake system (ABS), traction control and StabiliTrak for the duration of the ignition cycle.
* A DIC message and/or a warning indicator may be displayed.

Conditions for Clearing the DTC

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

Reference Information
Schematic Reference

Antilock Brake System Schematics [1][2]Antilock Brakes / Traction Control Systems
Connector End View Reference

Component Connector End Views Connector Views
Description and Operation

ABS Description and Operation Description and Operation
Electrical Information Reference

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Circuit Testing Circuit Testing
* Wiring Repairs Wiring Repairs
* Connector Repairs Connector Repairs

Scan Tool Reference

Control Module References Control Module Referencesfor scan tool information

Circuit/System Verification

Verify that no DTCs are set in the ECM.

If DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.