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 00: Cruise Control Brake Switch Circuit

### Circuit/System Description

The stop lamp switch signal circuit is a direct hardwire input to the engine control module (ECM) from the body control module (BCM). The ECM monitors the stop lamp switch signal circuit in order to detect when the brake pedal has been applied. When the brake pedal is pressed, the BCM sends a serial data message to the ECM indicating that the brake pedal has been applied. The BCM also sends a high voltage signal on the stop lamp switch signal circuit to the ECM. This DTC will set if the serial data message and the voltage signal on the stop lamp switch signal circuit do not match.

### 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.

### Conditions for Setting the DTC

• | The ECM detects that there is a 8.3 km/h (5.1 mph) or greater decrease in vehicle speed within 1 second.

• | The ECM detects that the class 2 serial data message and the voltage signal on the stop lamp switch signal circuit do not match for 10 consecutive times that this diagnostic is run.

• | The above condition is present for greater than 2 seconds.

### Action Taken When the DTC Sets

• | The cruise control system is disabled.

• | The ECM stores the DTC information into memory when the diagnostic runs and fails.

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

• | The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.

### Conditions for Clearing the DTC

• | A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.

• | A history DTC clears after 40 consecutive warm-up cycles, if failures are not reported by this or any other emission related diagnostic.

• | Use a scan tool in order to clear the DTC.

### Diagnostic Aids

In order to avoid a misdiagnosis, inspect for proper operation of the stop lamps. Refer to Exterior Lighting Systems Description and Operation .

For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections .

### Reference Information

#### Schematic Reference

• | Cruise Control Schematics

• | Exterior Lights Schematics

#### Connector End View Reference

• | Lighting Systems Connector End Views

• | Engine Controls Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Scan Tool Data List

### Circuit/System Testing

1. Ignition ON, verify that the Stop Lamp Pedal Switch parameter in the ECM reads Released while depressing the brake pedal.

⇒ | If the Stop Lamp Pedal Switch parameter reads Applied, replace the ECM.

2. Ignition OFF, test the stop lamp switch signal circuit for an open/high resistance, a short to ground or a short to voltage. If the circuit tests normal, replace the BCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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