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 P0572: Brake Switch Circuit 1 Low VoltageDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Brake Position Sensor Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09 |
Stop Lamp Relay Control | 1 | 1 | 1 | -- |
Stop Lamp Switch Signal | P0572 | P0573 | P0573 | -- |
Stop Lamp Relay Switch B+ | 1 | 1 | -- | -- |
Brake Position Sensor 5-Volt Reference | C0870 03 | C0870 03 | C0870 07 | -- |
Brake Position Sensor Low Reference | -- | C0277 06 | C0277 07 | -- |
Left Rear Stop/Turn Lamp Supply Voltage | 1 | 1 | 1 | -- |
Right Rear Stop/Turn Lamp Supply Voltage | 1 | 1 | 1 | -- |
Center High Mounted Stop Lamp (CHMSL) Ground | -- | 1 | 1 | -- |
Left Rear Stop/Turn Lamp Ground | -- | 1 | 1 | -- |
Right Rear Stop/Turn Lamp Ground | -- | 1 | 1 | -- |
1. Stop Lamps Malfunction | ||||
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, transmission control module (TCM), engine control module (ECM), and stop lamp relay coil side. The BCM also supplies the stop lamp relay coil with ground. When the stop lamp relay receives battery voltage and ground from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage through the STOP/B/U/LPS fuse to illuminate the center high mounted stop lamp (CHMSL).
Conditions for Running the DTC
| • | The ignition is in the ON position. |
| • | Battery voltage greater than 11.5 volts. |
Conditions for Setting the DTC
The ECM detects a short to ground on the signal circuit when the serial data message from the BCM indicates the brakes are applied.
Actions Taken When the DTC Sets
| • | The ECM stores the DTC to memory. |
| • | The ECM will record the operating conditions at the time the diagnostic failed. The ECM stores this information in Failure Records. |
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 40 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 .
Verify that the brake pedal position sensor is properly calibrated.
Reference Information
Schematic Reference
Connector End View Reference
Lighting Systems Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Ignition OFF, disconnect the C1 harness connector at the ECM.
- Connect a test lamp between the stop lamp switch signal circuit and ground.
- Ignition ON, command the stop lamp relay control ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, replace the ECM.
| ⇒ | If the test lamp is always OFF, test the control 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 and ECM replacement, setup, and programming |
