Diagnostic Instructions
DTC Descriptor
DTC P0571: Cruise Control Brake Switch Circuit
Diagnostic Fault Information
Circuit
| Short to Ground
| Open or High Resistance
| Short to Voltage
| Signal Performance
|
Stop Lamp Switch Signal
| P0571
| P0571
| P0571
| --
|
Circuit/System Description
The brake applied signal circuit is a high voltage input from the body control module (BCM) to the engine control module (ECM) and transmission control module (TCM). 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 brake applied 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 brake applied signal circuit when the brake pedal has been applied.
Conditions for Running the DTC
| • | The vehicle has cycled from 0-60 km/h (0-37 mph) 3 times in 1 ignition cycle. |
| • | Continuous once the previous criteria have been met. |
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 becomes 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
Cruise Control Schematics
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
Circuit/System Verification
Ignition ON, observe the Stoplamp Pedal Switch parameter while applying and releasing the brake pedal. The reading should change between Applied/Released, and all brake lights should turn ON and OFF accordingly. Refer to
Exterior Lighting Systems Description and Operation
Circuit/System Testing
- Ignition OFF, disconnect the harness connectors at the appropriate control modules listed below.
- Connect a test lamp between the appropriate signal circuit terminal listed below and ground.
- Ignition ON, press and release the brake pedal. Verify the test lamp turns ON and OFF when pressing and releasing the brake pedal.
| ⇒ | 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. |
- Ignition OFF, connect the harness connector at the TCM.
- Connect a test lamp between the appropriate signal circuit terminal listed below and ground.
| • | ECM X1 terminal 9 (L76) |
| • | ECM X2 terminal 52 (LY7) |
- Ignition ON, press and release the brake pedal. Verify the test lamp turns ON and OFF when pressing and releasing the brake pedal.
| ⇒ | If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the TCM. |
| ⇒ | 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 TCM. |
- If all circuits test normal, replace the ECM.
Repair Instructions
Perform the
Diagnostic Repair Verification.
