Circuit Description
C0240
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.
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 VSES. |
| • | The stability 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 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 DTCs function.
P1571
| • | The conditions for setting the DTC are no longer present and you use the scan tool Clear DTCs 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 - Engine Controls in Engine Controls - 4.8L, 5.3L and 6.0L in order to identify other possible causes of DTC C0298.
P1571
Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to Testing for Electrical Intermittents , Testing for Intermittent Conditions and Poor Connections , Connector Repairs and Wiring Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for voltage supplied to the EBCM from the PCM.
-
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 | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics Connector End View Reference: Antilock Brake System Connector End Views and Powertrain Control Module Connector End Views in Engine Controls - 4.8L, 5.3L and 6.0L | ||||
1 | Did you perform the ABS Diagnostic System Check? | -- | Go to Step 2 | |
2 | Is DTC P0856 set? | -- | Go to Step 3 | Go to Diagnostic Aids |
3 |
Does DTC P0856 reset? | -- | Go to Step 4 | Go to Diagnostic Aids |
Does the voltage measure greater than the specified value? | 4.75 V | Go to Step 5 | Go to Step 8 | |
Does the voltage measure less than the specified value? | 0.15 V | Go to Step 6 | Go to Step 9 | |
6 |
Does the Hz frequency of the requested torque signal measure within the specified range? | 121-134 Hz | Go to Step 7 | Go to Step 11 |
7 | Use the DMM in order to measure the duty cycle of the requested torque signal circuit. Does the duty cycle of the requested torque signal measure within the specified range? | 40-95% | Go to Step 12 | Go to Step 13 |
8 | Test the requested torque signal circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
9 | Test the requested torque signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 12 | |
10 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 |
11 | Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
12 |
Important: Perform the set up procedure for the PCM. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 4.8L, 5.3L and 6.0L. Did you complete the replacement? | -- | Go to Step 14 | -- |
13 |
Important: Following EBCM replacement, perform the set-up procedure for the EBCM and perform the Yaw Rate Reference Table Reset Procedure. Use the scan tool to perform the Tire Size Calibration procedure. Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does DTC P0856 reset? | -- | Go to Step 4 | System OK |
