P0856

DTC C0242 or P0856

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 C0242 71
- Engine Control Module (ECM) Indicated TCS Malfunction invalid serial data received.

DTC C0242 75
- Engine Control Module (ECM) Indicated TCS Malfunction signal above allowable range.

DTC P0856 00
- 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

* The ignition is ON.
* Ignition voltage is greater than 8 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 DTC P0856 and the EBCM will set C0242.

Action Taken When the DTC Sets

* The EBCM disables the TCS for the duration of the ignition cycle.
* The Traction Off indicator turns ON.
* The DIC displays the Service Traction Control message.
* The ABS remains functional.

Conditions for Clearing the DTC

* The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
* The electronic brake control module (EBCM) 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 ([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

* 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

Verify that no DTCs are set in the ECM.

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

Repair Instructions

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

Control Module References (Programming and Relearning)