Diagnostic Instructions
DTC Descriptors
DTC P0856: Engine Control Module (ECM) Indicated TCS Malfunction
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 9.6 volts.
Conditions for Setting the DTC
The ECM detects a fault that prevents it from performing a traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed.
Action Taken When the DTC Sets
| • | The EBCM disables the TCS for the duration of the ignition cycle. |
| • | The Traction Off indicator illuminates. |
| • | 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. |
| • | The electronic brake control module (EBCM) 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
Component Connector End Views
Description and Operation
ABS Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
Circuit/System Verification
Verify that no DTCs are set in the ECM.
