GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 CTS 🢒 Accessories 🢒 Navigation Systems 🢒 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 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 Input Signal

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The PCM diagnoses the requested torque signal circuit and sends a serial data message to the EBCM indicating that torque reduction is not allowed.

Action Taken When the DTC Sets
    • The EBCM disables the EDC/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 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.
    • The PCM automatically clears the history DTC when a current DTC is not detected in 40 consecutive warm-up cycles.

Diagnostic Aids

The following conditions can cause this concern:

    • An open in the delivered torque circuit.
    • An short to ground or voltage in the delivered torque circuit.
    • A wiring problem, terminal corrosion, or poor connection in the delivered torque circuit.
    • A communication frequency problem.
    • A communication duty cycle problem.
    • The EBCM is not receiving information from the ECM.
    • Loose or corroded EBCM ground or ECM ground.

Test Description

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

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

    2.

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

    3.

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

    4.

  4. This vehicle is equipped with a ECM which uses an electrically erasable programmable read only memory (EEPROM). When replacing the ECM, the replacement ECM must be programmed.

Step

Action

Values

Yes

No

Schematic Reference: Antilock Brake System Schematics

Connector End View Reference: Antilock Brake System Connector End Views , Engine Controls Connector End Views in Engine Controls - 3.6L, or Engine Controls Connector End Views in Engine Controls - 5.7L

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Start the engine.
  3. With a scan tool, observe the Torque Request Signal parameter in the Powertrain Control Module (PCM) data list.

Does the scan display less than the specified value?

100%

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the electronic brake control module (EBCM) harness connector.
  3. Install the J 39700 universal breakout box using the J 39700-300 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 frequency 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 J 39700-300 cable adapter from the EBCM connector.
  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 engine control module (ECM) 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 9

7
  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM) 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 the harness connector of the ECM. 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 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

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

Did you complete the replacement?

--

Go to Step 12

--

11

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

Did you complete the replacement?

--

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