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P0571



DTC P0571-P0573

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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 Voltage

DTC P0573
- Brake Switch Circuit 1 High Voltage

Diagnostic Fault Information






Circuit/System Description

The stop lamp switch signal circuit is a direct hardwire input to the engine control module (ECM), the transmission control module (TCM) and the center high mounted stop lamp (CHMSL). The modules monitor the stop lamp switch signal circuit to detect when the brake pedal has been applied. The BCM monitors the brake apply sensor signal circuit to determine when the brake pedal is applied. When the brake pedal is applied, the BCM sends a serial data message to the modules indicating that the brake pedal has been applied.

Conditions for Running the DTC

* The ignition is ON.
* The engine is running.
* Battery voltage is greater than 11.5 volts.

Conditions for Setting the DTC

P0572

The ECM detects a low voltage signal on the stop lamp switch signal circuit when the serial data message from the BCM indicates the brakes are applied.

P0573

The ECM detects 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.

Action 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.
* The cruise control system becomes inoperative.

Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 40 malfunction-free ignition cycles have occurred.

Circuit/System Verification

Inspect for proper operation of the stop lamps, including the CHMSL.

Circuit/System Testing

1. Ignition OFF, disconnect the CHMSL relay.
2. Connect a test lamp between the signal circuit terminal 85 and ground.
3. 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.

4. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal 86 and B+.

• If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

5. Ignition OFF, connect the CHMSL relay.
6. Ignition OFF, disconnect the harness connectors at the control modules ECM X1 (L61 or LE5) or X2 (LNF) and the TCM.
7. Connect a test lamp between the TCM harness connector terminal 42 and ground.
8. 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, test or replace the CHMSL relay.
• If the test lamp is always OFF, test the signal circuit and the CHMSL fuse circuit for a short to ground or an open/high resistance. If the circuits tests normal, test or replace the CHMSL relay.

9. Ignition OFF, connect the harness connector at the TCM.
10. Connect a test lamp between the appropriate signal circuit terminal listed below and ground.

* ECM harness connector X1 terminal 55 (L61 or LE5)
* ECM harness connector X1 terminal 52 (LNF)

11. 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 an open/high resistance. If the circuit tests normal, replace the TCM.

12. If all circuit tests normal, replace the ECM.

Component Testing

Relay Test

1. Ignition OFF, disconnect the CHMSL relay.
2. Test for 60-180 ohms of resistance between terminals 85 and 86.

• If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87

• If less than infinite resistance, replace the CHMSL relay.

4. 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 CHMSL relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
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