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
- Engine Control Module (ECM) Indicated TCS Malfunction

DTC P0856
- Engine Control Module (ECM) 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 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.

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 and the EBCM will set this DTC.

Action Taken When the DTC Sets

* The EBCM disables the traction control system (TCS) for the duration of the ignition cycle.
* The Traction Off indicator illuminates.
* The message center displays the Service Traction System message.
* The antilock brake system (ABS) remains functional.

Conditions for Clearing the DTC

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

Diagnostic Aids

These DTCs are an indicator that the ECM receives an invalid message from the EBCM and does not necessarily indicate a fault is present with the EBCM. This DTC should not be used as a fault indicator, but rather as a symptom to assist in the diagnosis of these other systems.

Reference Information
Schematic Reference

Antilock Brake System Schematics (without HP7) ([1][2]Antilock Brakes / Traction Control Systems)Antilock Brake System Schematics (HP7) ([1][2]Antilock Brakes / Traction Control Systems)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

ABS Description and Operation (with LAT) ()
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).