C1277

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.

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. The PCM will set DTC P1571 and the EBCM will set DTC C1277. 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
^ The EBCM disables the TCS for the duration of the ignition cycle.
^ The TRACTION OFF indicator turns ON.
^ The 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.

Diagnostic Aids
The following conditions can cause this concern:
^ An open in the requested torque circuit.
^ An short to ground or voltage in the requested torque circuit.
^ A wiring problem, terminal corrosion, or poor connection in the requested torque circuit.
^ A communication frequency problem.
^ A communication duty cycle problem.
^ The PCM is not receiving information from the EBCM.
^ Loose or corroded EBCM ground or PCM ground.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
4. This step uses the scan tool to determine whether the requested torque signal has a valid duty cycle.
5. This step measures whether the requested torque signal has a valid duty cycle.
6. This step measures whether the requested torque signal has a valid frequency.