Diagnostic Instructions
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
| • | 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:
Scan Tool Reference:
Circuit/System Verification
Verify that no DTCs are set in the ECM.
