Service Information

Volt

DTC P0571

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

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 brake 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 brake lamp switch signal circuit when the serial data message from the ECM indicates the brakes are applied, or a high voltage signal on the brake 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

Vehicle OFF, disconnect the X1 harness connector as the ECM.
Connect a test lamp between the control circuit terminal 33 and ground.
Vehicle in Service Mode, verify the test lamp turns ON and OFF when pressing and releasing the brake pedal.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

If all test normal, replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

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