P0856

DTC C0240 or P0856
DTC Descriptor
DTC C0240
PCM Traction Control Not Allowed

DTC P0856
Traction Control Torque Request Circuit

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Diagnostic System Check - Vehicle

Circuit/System Description
C0240
The powertrain control module (PCM) and the electronic brake control module (EBCM) communicate on the serial data link, whenever the ignition is ON.

P0856
The PCM supplies 5 volts through an internal resistor, to the EBCM on the requested torque signal circuit. The EBCM toggles this voltage to ground to create a valid requested torque signal at the PCM.

Conditions for Running the DTC
C0240
The ignition is ON.

P0856
^ The ignition is ON.
^ The engine is running at a speed greater than 450 RPM for 5 - 20 seconds.

Conditions for Setting the DTC
C0240
The EBCM receives a serial data message stating that the PCM has lost the ability to reduce engine torque.

P0856
The PCM receives an invalid requested torque signal for 3 seconds.

Action Taken When the DTC Sets
C0240
^ The EBCM disables the traction control system (TCS) and vehicle stability enhancement system (VSES).
^ The TRACTION FAILED message is displayed.

P0856
^ The PCM sends a serial data message to the EBCM stating that the PCM has lost the ability to reduce engine torque.
^ The EBCM sets DTC C0240 as a current DTC for as long as the malfunction is present.

Conditions for Clearing the DTC
C0240
The conditions for setting the DTC are no longer present and you use the scan tool Clear DTC's function.

P0856
^ The conditions for setting the DTC are no longer present and you use the scan tool Clear DTC's function.
^ A history DTC clears automatically after 40 consecutive warm-up cycles without a PCM detected failure.

Diagnostic Aids
C0240
A requested torque signal malfunction is only one possible cause for the PCM to lose the ability to perform traction control. DTC C0240 may set due to engine overheating, throttle actuator control failure, loss of ignition timing control by the PCM, etc. If DTC P1571 has not set, refer to Diagnostic System Check - Vehicle to identify other possible causes of DTC C0240. Diagnostic System Check - Vehicle

P0856
Thoroughly inspect connections or circuitry that may cause an intermittent malfunction.

Reference Information
Schematic Reference
ABS Schematics

Connector End View Reference
^ ABS Connector End Views
^ Powertrain Control Module (PCM) Connector End Views

Electrical Information Reference
^ Circuit Testing
^ Connector Repairs
^ Testing for Intermittent Conditions and Poor Connections
^ Wiring Repairs

Scan Tool Reference
Scan Tool Data List

Circuit/System Testing
1. Use a scan tool in order to clear the DTC's. Cycle the ignition to OFF and then start the engine. A current failure will set a DTC.
^ If the DTC does not reset, go to Diagnostic Aids. Component Tests and General Diagnostics

2. Turn OFF the ignition and disconnect the EBCM harness connector. At the EBCM harness connector, use a DMM to measure for 5 volts on the requested torque circuit. Turn ON the ignition.
^ If the voltage is below 4.5 volts, check for an open or short to ground on the requested torque circuit.
^ If the voltage is below 4.5 volts and an open or short to ground cannot be found, replace the EBCM/brake pressure modulator valve (BPMV) assembly.

3. Connect one end of a test lamp to ground. With the DMM still connected to the EBCM harness connector, touch the other end of the test lamp to the DMM lead connected to the EBCM harness connector. The DMM voltage reading should drop below 0.15 volts.
^ If the voltage does not drop to below 0.15 volts, check for a short to voltage on the requested torque circuit. If a short to voltage cannot be found, replace the PCM.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Control Module References for EBCM or PCM replacement, setup, and programming