GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.

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 a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.

The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.

When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

C1276

One of the following conditions exists:

    • The EBCM detects that delivered torque signal is out of the valid range.
    • The EBCM does not receive the delivered torque signal.

P1644 or P1689

The PCM detects that the delivered torque signal voltage is invalid.

Action Taken When the DTC Sets

    • The EBCM disables the TCS for the duration of the ignition cycle.
    • The PCM will store conditions which were present when the DTC set as Fail Records data only.
    • The Traction Control 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 condition for the DTC is no longer present (the DTC is not current) and you used the On-Board Diagnostics Clear DTC function.
    • The EBCM automatically clears the history DTC when a current DTC is not detected in 50 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 PCM.
    • Loose or corroded EBCM ground or PCM 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 delivered torque signal has a valid duty cycle.

  2. 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

Values

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the ABS Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - ABS

2

Inspect the EBCM ground and PCM ground, making sure each ground is clean and torqued to the proper specification. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 3

3

  1. Install a scan tool.
  2. Start the engine.
  3. With a scan tool, observe the Delivered Torque parameter in the Delco/Bosch ABS/TCS ICCS (if equipped) data list.

Does the scan tool display the specified range?

90%

Go to Step 4

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

4

  1. Turn OFF the ignition.
  2. Disconnect the EBCM harness connector.
  3. Install the J 39700 universal pinout box using the J 39700-25 cable adapter to the EBCM harness connector and the EBCM connector.
  4. Disconnect the powertrain control module (PCM) harness connector.
  5. Turn ON the ignition, with the engine OFF.
  6. Measure the voltage from the delivered torque signal circuit to a good ground.

Does the voltage measure near the specified value?

B+

Go to Step 5

Go to Step 6

5

  1. Turn OFF the ignition.
  2. Disconnect the J 39700-25 cable adapter from the EBCM connector.
  3. Turn ON the engine, with the engine OFF.
  4. Test the delivered 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 11

Go to Step 7

6

  1. Turn OFF the ignition.
  2. Disconnect the J 39700-25 cable adapter from the EBCM connector.
  3. Test the delivered torque signal circuit for the following conditions:
  4. • An open
    • A short to ground
    • A high resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

7

Inspect for poor connections 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 11

Go to Step 9

8

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 11

Go to Step 10

9

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 4.6L.

Did you complete the repair?

--

Go to Step 11

--

10

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

Did you complete the repair?

--

Go to Step 11

--

11

  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