C0242

DTC C0242 or P0856

Diagnostic Instructions

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

DTC Descriptors

DTC C0242
- ECM Indicated TCS Malfunction

DTC P0856
- TCS Inhibited

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 high speed GMLAN serial data message to the EBCM indicating that torque reduction is not allowed. The ECM will typically set DTC P0856 in addition to other DTCs and the EBCM will set DTC C0242.

Action Taken When the DTC Sets

* The EBCM disables the traction control system (TCS) for the duration of the ignition cycle.
* The traction control off indicator turns on.
* The antilock brake system (ABS) remains functional.

Conditions for Clearing the DTC

* The condition for setting 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

Connector End View Reference:

Antilock Brake System Connector End Views

Description and Operation:

ABS Description and Operation

Electrical Information Reference:

* Testing for Intermittent Conditions and Poor Connections in Diagnostic Aids
* Circuit Testing

Scan Tool Reference:

* Scan Tool Output Controls
* Scan Tool Data List
* Scan Tool Data Definitions

Circuit/System Verification

Verify that no DTCs are set in the ECM.

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