For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0856 00: Traction Control Torque Request Circuit Malfunction

### Circuit/System Description

When traction control is active, the electronic brake control module (EBCM) sends a serial data message to the engine control module (ECM) requesting torque reduction. When certain ECM DTCs are set, the ECM will not be able to perform the torque reduction for traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

### Conditions for Running the DTC

Engine running

### Conditions for Setting the DTC

The ECM detects a fault that prevents it from performing a traction control function 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 traction control and stability control for the duration of the ignition cycle.

• | The traction control/stability control-active indicator turns ON.

### Conditions for Clearing the DTC

• | A current DTC clears when the diagnostic runs and passes.

• | The EBCM will turn OFF the indicator in the next ignition cycle.

### Reference Information

#### Schematic Reference

Antilock Brake System Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

ABS Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Verify that no DTCs except P0856 00 are present in the ECM.

⇒ | If any DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle

2. Replace the K20 Engine Control Module (ECM) and verify the DTC does not reset.

⇒ | If the DTC resets replace the K17 Electronic Brake Control Module (EBCM).

### Repair Instructions

• | Perform the Diagnostic Repair Verification

• | Control Module References