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 P0504: Brake Switch Circuit 1-2 CorrelationDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Stop Lamp Switch Signal | B3445, P0573 | P0573 | P0572 | P0504 |
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
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References 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 . |
Circuit/System Testing
- Ignition OFF, disconnect the X2 harness connector at the ECM.
- Connect a test lamp between the signal circuit terminal 10 and ground.
- Ignition ON, press and release the brake pedal. The test lamp should turn ON and OFF when pressing and releasing the brake pedal.
- If all circuits test normal, replace the ECM.
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for BCM or ECM replacement, setup, and programming
