Diagnostic Instructions
DTC Descriptor
DTC P0571 00: Cruise Control Brake Switch Circuit
Circuit/System Description
The brake switch signal circuit is a high voltage input to the body control module (BCM), engine control module (ECM) and transmission control module (TCM). The BCM monitors the stop lamp switch circuit to detect when the brake pedal has been applied.
The ECM monitors the brake switch signal to determine when the brake pedal is applied. When the brake pedal is applied, the BCM sends a GMLAN 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.
Conditions for Running the DTC
| • | Battery voltage is greater than 11.5 volts. |
Conditions for Setting the DTC
The ECM detects a low voltage signal on the brake switch signal circuit when the serial data message from the BCM indicates the brakes are applied.
Action Taken When the DTC Sets
| • | The cruise control system becomes inoperative. |
| • | 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
| • | A last test failed, or the current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if failures are not reported by this or any other emission related diagnostic. |
Reference Information
Schematic Reference
Exterior Lights Schematics
Connector End View Reference
Lighting Systems Connector End Views
Description and Operation
Cruise Control Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Ignition OFF, disconnect the harness connector of the stop lamp switch.
- Ignition ON, verify that a test lamp illuminates between the stop lamp switch voltage circuit terminal B and ground.
| ⇒ | If the test lamp does not illuminate, test the stop lamp switch voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the RUN/CRANK Relay. |
- Ignition OFF, disconnect the harness connectors of the BCM C5, ECM C1, and the TCM.
- Ignition OFF, verify that a test lamp does not illuminate between the stop lamp switch TCC brake signal circuit terminal A and B+.
| ⇒ | If the test lamp illuminates, test the TCC brake signal circuit for a short to ground. |
- Ignition ON, verify that a test lamp does not illuminate between the stop lamp switch TCC brake signal circuit terminal A and ground.
| ⇒ | If the test lamp illuminates, test the TCC brake signal circuit for a short to voltage. |
- If all circuits test normal, replace the stop lamp switch.
Component Testing
Relay Test
- Ignition OFF, disconnect the RUN/CRANK relay.
- Test for 60-180 ohms of resistance between terminals 85 and 86.
| ⇒ | If the resistance is not within the specified range, replace the relay. |
- Test for infinite resistance between the following terminals:
| ⇒ | If less than infinite resistance, replace the RUN/CRANK relay. |
- Install a 20-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2.0 ohms of resistance between terminals 30 and 87.
| ⇒ | If greater than 2.0 ohms, replace the RUN/CRANK relay. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
