The stop lamp switch signal circuit is a high voltage input to the body control module (BCM), engine control module (ECM), transmission control module (TCM), Power Take Off (PTO) module (if equipped) and Trailer Brake controller (if equipped). The BCM monitors the stop lamp switch circuit to detect when the brake pedal has been applied. The ECM monitors the stop lamp switch signal to determine when the brake pedal is applied. When the brake pedal is applied, the BCM 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 switch signal circuit when the stop lamp switch is closed.

P0572

The ECM detects a low voltage signal on the stop lamp switch signal circuit for more than 2 seconds when the serial data message from the BCM indicates the brakes are applied. The ECM sets the DTC when the condition has been detected 8 out of 10 times.

P0573

The ECM detects a high voltage signal on the stop lamp switch signal circuit for more than 2 seconds when the serial data message from the BCM indicates the brakes are released. The ECM sets the DTC when the condition has been detected 8 out of 10 times.

Ensure all the stop lamps operate properly. Refer to Exterior Lighting Systems Description and Operation to avoid misdiagnosis. If the vehicle stop lamps operate improperly, refer to Symptoms - Lighting.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Cruise Control Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, test for B+ between the B+ circuit terminal B and ground.

⇒	If less than the specified value, test the B+ circuit for a short to ground or an open/high resistance.

3. Verify the BPP Circuit Signal data parameter displays released.

⇒	If not the specified value, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Connect a 3A fused jumper between the B+ circuit terminal B and the signal circuit terminal A. Verify the BPP Circuit Signal data parameter displays applied.

⇒	If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the stop lamp switch.

1. Ignition OFF, disconnect the stop lamp switch.
2. With the brake pedal released, test for infinite resistance between terminal A and terminal B stop lamp switch.

⇒	If not the specified value, replace the stop lamp switch.

3. With the brake pedal released, test for less than 1.0 ohm between terminal C and terminal D at the stop lamp switch.

⇒	If not the specified value, replace the stop lamp switch.

4. With the brake pedal applied, test for less than 1.0 ohm between terminal A and terminal B at the stop lamp switch.

⇒	If not the specified value, replace the stop lamp switch.

5. With the brake pedal applied, test for infinite resistance between terminal C and terminal D at the stop lamp switch.

⇒	If not the specified value, replace the stop lamp switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.