P0856

DTC C0298 or P0856
Circuit Description
C0298
The powertrain control module (PCM) and the electronic brake control module (EBCM) communicate on the serial data line 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 the requested torque signal.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C0298 Powertrain Control Malfunction

Conditions for Running the DTC
C0298
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
C0298
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
C0298
^ The EBCM disables the traction control system (TCS).
^ The traction off indicator turns ON.

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 C0298 or DTC C0240 as a current DTC for as long as the malfunction is present.

Conditions for Clearing the DTC
C0298
The conditions for setting the DTC are no longer present and you use the scan tool Clear DTC's function.

P1571
^ 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
C0298
A requested torque signal malfunction is only one possible cause for the PCM to lose the ability to perform traction control. DTC C0298 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 in order to identify other possible causes of DTC C0298. Testing and Inspection

P1571
Thoroughly inspect connections or circuitry that may cause an intermittent malfunction.
Refer to the following:
^ Testing for Intermittent Conditions and Poor Connections Component Tests and General Diagnostics
^ Connector Repairs
^ Wiring Repairs

Test Description
The numbers below refer to the step numbers on the diagnostic table.
4. This step tests for voltage supplied to the EBCM from the PCM.
5. This step tests for a shorted resistor in the PCM, or a short to voltage within the requested torque circuit, by verifying that a large voltage drop occurs when a test lamp is connected in parallel with the DMM.

Step 1 - Step 10:

Step 11 - Step 14: