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 P0571: Cruise Control Brake Switch Circuit

### Circuit/System Description

The brake applied signal circuit is a high voltage input from the body control module (BCM) to the engine control module (ECM) and transmission control module (TCM). The ECM monitors the stop lamp switch circuit to detect when the brake pedal has been applied. The BCM monitors the brake pedal position sensor to determine when the brake pedal is applied. When the brake pedal is applied, the BCM supplies a high voltage signal on the brake applied signal circuit and also sends a serial data message to the ECM indicating that the brake pedal has been applied. The ECM senses a high voltage signal on the brake applied signal circuit when the brake pedal has been applied.

### Conditions for Running the DTC

• | The engine speed is greater than 700 RPM.

• | The traction control system or the antilock brake system are not active and have not failed.

• | The vehicle speed is greater than 48 km/h (30 mph).

• | The diagnostic will disable when the wheel speed is less than 16 km/h (10 mph).

### Conditions for Setting the DTC

The ECM detects either a low voltage signal on the stop lamp switch signal circuit when the serial data message from the BCM indicates the brakes are applied, or a high voltage signal on the stop lamp switch signal circuit when the serial data message from the BCM indicates the brakes are not applied.

### Actions Taken When the DTC Sets

• | The malfunction indicator lamp (MIL) will not illuminate.

• | The cruise control system becomes disabled.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC not longer exists.

• | A history DTC will clear after 40 malfunction-free ignition cycles have occurred.

### Reference Information

#### Schematic Reference

Exterior Lights Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Cruise Control 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 Verification

Ignition ON, observe the Stoplamp Pedal Switch parameter while applying and releasing the brake pedal. The reading should change between Applied/Released, and all brake lights should turn ON and OFF accordingly. Refer to Exterior Lighting Systems Description and Operation

### Circuit/System Verification

1. Verify that DTC P0572 or P0573 is not set.

⇒ | If DTC is set, refer to Diagnostic System Check - Vehicle.

2. Verify that DTC P0571 is not set.

⇒ | If DTC is set, replace the BCM. Clear the DTC and road test the vehicle. If DTC resets, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM or ECM replacement, setup, and programming