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 Descriptors
DTC P0572: Brake Switch Circuit 1 Low VoltageDTC P0573: Brake Switch Circuit 1 High Voltage
Diagnostic Fault Information
Circuit | Short to Ground | Open or High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Stop Lamp Switch Signal | P0572 | P0572 | P0573 | P0572 or P0573 |
Circuit/System Description
The stop lamp switch signal circuit is a high voltage input from the body control module (BCM) to the engine control module (ECM). The ECM monitors the stop lamp switch circuit to detect when the brake pedal has been applied. The BCM monitors the brake pedal position sensor to determine when the brake pedal is applied. When the brake pedal is applied, the BCM supplies a high voltage signal on the stop lamp switch signal circuit and also 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 stop lamp switch signal circuit when the brake pedal has been applied.
Conditions for Running the DTC
| • | The engine is running. |
| • | Battery voltage is greater than 11.5 volts. |
Conditions for Setting the DTC
The ECM detects either a low voltage signal on the stop lamp switch signal circuit when the serial data message from the BCM indicates the brakes are applied, or a high voltage signal on the stop lamp switch signal circuit when the serial data message from the BCM indicates the brakes are not applied.
Actions Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The cruise control system is disabled. |
Conditions for Clearing the DTC
| • | The condition responsible for setting the DTC no longer exists. |
| • | A history DTC will clear after 40 malfunction-free ignition cycles have occurred. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Cruise Control Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- Ignition OFF, disconnect the X1 harness connector at the K20 ECM.
- Connect a test lamp between the appropriate signal circuit terminal listed below and ground.
- Ignition ON, verify the test lamp turns ON and OFF when pressing and releasing the brake pedal.
- If all circuits test normal, replace the K20 ECM.
| • | terminal 85 (LLU) |
| • | terminal 25 (LDE/2H0) |
| ⇒ | If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K9 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 K9 BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for BCM, ECM, replacement, setup, and programming
