P0856

DTC C0241 or P0856

Circuit Description

The EBCM and the PCM simultaneously control the traction control. The EBCM sends a Requested Torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. The PCM supplies the pull up voltage that the EBCM switches to ground to create the signal.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

* DTC C0241 Powertrain Control Module (PCM) Indicated Requested Torque Malfunction
* DTC P0856 Traction Control Torque Request Circuit

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The PCM diagnoses the requested torque PWM signal circuit and sends a class 2 serial data message to the EBCM indicating a fault is present. A fault exists in the circuit if the PCM detects one of the following conditions:

* The requested torque PWM signal is less than 5 percent duty cycle or greater than 95 percent duty cycle.
* The requested torque PWM signal is not present for 10 seconds.

Action Taken When the DTC Sets

If equipped, the following actions occur:

* The electronic brake control module (EBCM) disables the traction control system (TCS)/vehicle stability enhancement system (VSES) for the duration of the ignition cycle.
* A malfunction DTC will set.
* The Stability Off indicator turns ON.
* The antilock brake system (ABS) remains functional.

Conditions for Clearing the DTC

* The condition for the DTC is no longer present (the DTC is not current) and you used the scan tool Clear DTC function.
* The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

3. Use the scan tool in order to determine if the requested torque signal has a valid duty cycle.
4. Measure the requested torque signal in order to determine if the signal has a valid duty cycle.
5. Measure the requested torque signal in order to determine if the signal has a valid frequency.
11. This vehicle is equipped with a PCM which uses an electrically erasable programmable read only memory (EEPROM). When replacing the PCM, the replacement PCM must be programmed.

Step 1 - Step 8:

Step 9 - Step 13: