For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using the 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 C0161 00: Antilock Brake System (ABS) Brake Switch Circuit

### Circuit/System Description

The normally-open stop lamp switch supplies battery voltage to the engine control module (ECM) when the brake pedal is pressed. The ECM sends a brake pedal applied serial data message to the electronic brake and traction control module (EBTCM) and to the transmission control module (TCM).

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

• | The EBCM detects an open in the brake signal circuit.

• | Both brake lamps are faulty.

### Action Taken When the DTC Sets

• | The EBCM stores this information only code DTC for as long as the condition is present.

• | The ABS remains functional.

### Conditions for Clearing the DTC

• | The condition for the DTC is no longer present.

• | The DTC is cleared with a scan tool.

• | The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

### Diagnostic Aids

• | A signal circuit of the stop lamp switch is open

• | The stop lamp switch is improperly adjusted

• | All brake lamps are open

• | All brake lamp grounds are open

• | An open or high resistance in the EBCM ground

### Reference Information

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Scan Tool Data List for EBCM

### Circuit/System Verification

1. Apply and release brake pedal. Verify brake lamps operate properly.

⇒ | If brake lamps do not operate properly, refer to Diagnostic Starting Point - Lighting Systems .

2. Replace EBCM/brake pressure modulator valve (BPMV) assembly.

### Repair Verification

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.