P0504

DTC P0504

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 P0504
- Brake Switch Circuit 1-2 Correlation




Diagnostic Fault Information






Circuit/System Description

When the brake pedal is applied, the BCM receives a brake applied signal from the brake pedal position sensor (BPPS). The BCM applies B+ to the stop lamp switch signal circuit. This circuit supplies a B+ signal to the engine control module (ECM) (LY7), transmission control module (TCM) (LY7), throttle actuator control (TAC) module, and electronic brake control module (EBCM) indicating the brakes are applied. B+ is also supplied to the center high mound stop lamp (CHMSL), illuminating it when the brakes are depressed. The BCM also reports the status of the brake pedal on the serial data line. The ECM monitors both the stop lamp switch signal circuit and the serial data message from the BCM to ensure that they are the same.


Conditions for Running the DTC

The ignition is ON.


Conditions for Setting the DTC

The voltage value seen on the stop lamp switch signal circuit at the ECM and the brake pedal status report by the BCM do not match.


Action Taken When the DTC Sets

* Stop lamp switch input is ignored. Brake apply status is obtained exclusively through serial data messages.
* Cruise control is disabled.



Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.



Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems 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, depress the brake pedal. The stop lamps should illuminate.

If the stop lamps do not illuminate, refer to Stop Lamps Malfunction (Stop Lamps Malfunction).



Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the ECM.
2. Connect a test lamp between the signal circuit terminal 10 and ground.
3. Ignition ON, press and release the brake pedal. The test lamp should turn 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. If all circuits test normal, replace the ECM.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.


Control Module References (Programming and Relearning) for BCM or ECM replacement, setup, and programming