GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Rendezvous - FWD 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C0241 or P0856

Circuit Description

The electronic brake control module (EBCM) and the powertrain control module (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 10-90 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 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 EBCM disables the traction control module (TCS) for the duration of the ignition cycle.
    • A malfunction DTC will set.
    • 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.

Test Description

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

  1. Measure the requested torque signal in order to determine if the signal has a valid duty cycle.

    2.

  2. Measure the requested torque signal in order to determine if the signal has a valid frequency.

    3.

  3. 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

Action

Value(s)

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?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Inspect the electronic brake control module (EBCM) ground and powertrain control module (PCM) ground, making sure each ground is clean and torqued to the proper specification. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the EBCM harness connector.
  3. Install the J 39700 Universal Breakout Box using the J 39700-530 Cable Adapter to the EBCM harness connector and the EBCM connector.
  4. Start the engine.
  5. Measure the DC duty cycle between the requested torque signal circuit and a good ground.

Is the duty cycle within the specified range?

5-95%

Go to Step 4

Go to Step 5

4

Measure the DC Hz between the requested torque signal circuit and a good ground.

Does the frequency measure within the specified range?

121-134 Hz

Go to Step 7

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the cable adapter from the EBCM connector.

    3. Important: Disconnecting the EBCM connector and turning ON the ignition could cause other modules to set loss of communication DTCs (Uxxxx). Once the EBCM is reconnected, the EBCM may set DTC C0241.

  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the requested torque signal circuit to a good ground.

Does the voltage measure within the specified range?

4-6 V

Go to Step 9

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Disconnect the PCM harness connector.
  3. Test the requested torque signal circuit for the following conditions:
    4. • A short to voltage
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

7
  1. Turn OFF the ignition.
  2. Disconnect the PCM harness connector.
  3. Test the requested torque signal circuit for the following conditions:
    4. • An open
    • A high resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8

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 12

Go to Step 10

9

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 12

Go to Step 11

10

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the repair?

--

Go to Step 12

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11

Replace the EBCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the repair?

--

Go to Step 12

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12
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK