Circuit Description
C0298
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 the requested torque signal at the PCM.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC C0298 Powertrain Control Malfunction |
| • | DTC P0856 Traction Control Torque Request Circuit |
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 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.
P0856
| • | 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 P0856 has not set, refer to the following in order to identify other possible causes of DTC C0298:
| • | Symptoms - Engine Controls for the 4.3L engine |
| • | Symptoms - Engine Controls for the 8.1L engine |
| • | Symptoms - Engine Controls for the 4.8L, 5.3L, and 6.0L engines |
| • | Symptoms - Engine Controls for the 6.6L (LBZ and LLY) engine |
P0856
Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to following:
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 | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 | If DTCs set for the Parallel Hybrid Truck (PHT), C0035 or U0415, C0055 or C003D, C0245 or C0078, and C0550 or C0570, diagnose these DTC first. Is only DTC P0856 set? | -- | Go to Step 3 | Go to Diagnostic Aids |
3 |
| -- | 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 . 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 . 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 powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . 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 . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
12 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the EBCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does DTC P0856 reset? | -- | Go to Step 4 | System OK |
