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 Off indicator turns ON. |
| • | The message center displays the Service Traction System message. |
| • | 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 PCM. |
| • | Loose or corroded EBCM ground or PCM ground. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for voltage supplied to the PCM from the EBCM.
-
The PCM may be damaged if the delivered torque signal circuit is shorted to voltage.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics Connector End View Reference: Antilock Brake System Connector End Views , or Powertrain Control Module Connector End Views in Engine Controls-3.4 L, or Powertrain Control Module Connector End Views in Engine Controls-3.8 L | ||||
1 | Did you perform the ABS Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the DTC set? | -- | Go to Step 3 | Go to Diagnostic Aids |
Does the voltage measure within the specified range? | 13-10.5 V | Go to Step 5 | Go to Step 4 | |
4 | Test the delivered 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 12 | Go to Step 7 |
5 |
Does the scan tool display the duty cycle of the delivered torque signal display the specified value? | 5-95% | Go to Step 6 | Go to Step 9 |
6 |
Does the frequency of the delivered torque signal measure within the specified range? | 121-134 Hz | Go to Step 7 | Go to Step 9 |
7 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 |
8 | Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Did you complete the repair? | -- | Go to Step 12 | -- |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | |
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 12 | Go to Step 11 |
11 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 3.4L or Powertrain Control Module Replacement in Engine Controls - 3.8L. Did you complete the repair? | -- | Go to Step 12 | -- |
12 |
Does the DTC reset? | -- | Go to Step 3 | System OK |
