B3903

DTC B3903

DTC DESCRIPTOR

DTC B3903 02
Stop Lamp Relay Circuit Short to Ground

DTC B3903 05
Stop Lamp Relay Circuit Open or Short to Voltage




DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery positive voltage to the stop lamps, center high mounted stop lamp (CHMSL), transmission control module (TCM), and engine control module (ECM). The stop lamps will not operate unless the ignition is in the ON position.

CONDITIONS FOR RUNNING THE DTC
Battery voltage must be between 9-16 volts.

CONDITIONS FOR SETTING THE DTC

DTC B3903 02
This DTC will set when the BCM detects a short to ground in the stop lamp switch signal circuit.

DTC B3903 05
This DTC will set when the BCM detects an open or short to voltage in the stop lamp switch signal circuit.

ACTION TAKEN WHEN THE DTC SETS
When DTC B3903 is present, the service vehicle soon indicator will illuminate.

CONDITIONS FOR CLEARING THE DTC
- The condition responsible for setting the DTC no longer exists.
- You issue a scan tool CLEAR DTCs command.
- A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

DIAGNOSTIC AIDS

IMPORTANT: The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation.

CIRCUIT/SYSTEM TESTING

DTC B3903 02
1. Ignition OFF.
- Test the stop lamp switch signal circuit for a short to ground.
2. If all circuits test normal, replace the BCM.

DTC B3903 05
1. Ignition OFF.
- Test the stop lamp switch signal circuit for a short to voltage or an open/high resistance.
2. If all circuits test normal, replace the BCM.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Control Module References for BCM replacement, setup, and programming