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 engine control module (ECM) monitors the brake pedal position sensor. When the brake pedal is applied, the ECM detects a predetermined voltage signal. The ECM sends a serial data message to the engine control module (BCM) indicating the status of the stop lamps.

This diagnostic test functions on the assumption that a sudden decrease in vehicle speed is caused by a brake pedal application. When the ECM detects that there is a 4.2 km/h (2.6 mph) or greater decrease in vehicle speed within 0.25 seconds without a transition of the stop lamp switch, the ECM sets DTC P0571.

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

### Actions Taken When the DTC Sets

• | The cruise control system is disabled.

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

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

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

### Reference Information

#### Schematic Reference

• | Cruise Control Schematics

• | Exterior Lights Schematics

• | Antilock Brake System 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

1. Verify that DTC B3445 or B3878 is not set.

⇒ | If DTC is set, refer to DTC B3445 or B3878

2. Verify that DTC P0571 is not set.

⇒ | If DTC is set, replace the K20 ECM. Clear the DTC and road test the vehicle. If DTC resets, replace the K9 BCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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