P0571

DTC P0571

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category



DTC Descriptor
DTC P0571
- Cruise Control Brake Switch Circuit




Diagnostic Fault Information






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 vehicle has cycled from 0-60 km/h (0-37 mph) 3 times in 1 ignition cycle.
* Continuous once the previous criteria have been met.



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 no longer exists.
* A history DTC will clear after 40 malfunction-free ignition cycles have occurred.



Reference Information
Schematic Reference

Cruise Control Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Cruise Control Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) 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 (Exterior Lighting Systems Description and Operation)


Circuit/System Testing

1. Ignition OFF, disconnect the harness connectors at the appropriate control modules listed below.

* ECM X1 (L76)
* ECM X2 (LY7)
* TCM

2. Connect a test lamp between the appropriate signal circuit terminal listed below and ground.

* ECM terminal 9 (L76)
* ECM terminal 52 (LY7)
* TCM terminal 6 (L76)
* TCM terminal 38 (LY7)

3. Ignition ON, press and release the brake pedal. Verify the test lamp turns ON and OFF when pressing and releasing the brake pedal.

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

4. Ignition OFF, connect the harness connector at the TCM.
5. Connect a test lamp between the appropriate signal circuit terminal listed below and ground.

* ECM X1 terminal 9 (L76)
* ECM X2 terminal 52 (LY7)

6. Ignition ON, press and release the brake pedal. Verify the test lamp turns ON and OFF when pressing and releasing the brake pedal.

• If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the TCM.
• If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the TCM.

7. If all circuits test normal, replace the ECM.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) .

* Stop Lamp Switch Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM, ECM, TCM or automatic transmission control replacement, setup, and programming