Allison - Automatic Transmission

DTC P0571

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.

DTC Descriptor
DTC P0571
- Brake Switch Circuit 1

Circuit/System Description

The body control module (BCM) is constantly monitoring the status of the brake switch. The BCM sends the status of the brake switch out on the serial data line to other control modules. The TCM monitors the status of the brake switch and output speed of the transmission and determines if the brake switch is ON or OFF during a vehicle acceleration or deceleration event.

Conditions for Running the DTC

* DTC P0721, P0722, or P0751 is not set.
* Battery voltage is between 9-18 volts.
* The engine speed is greater than 200 RPM for 5 seconds.

Conditions for Setting the DTC

Condition 1

The TCM detects 10 vehicle acceleration events with the brake switch ON, and the brake switch has not changed states.

Condition 2

The TCM detects 10 vehicle deceleration events to a stops with the brake switch OFF, and the brake switch has not changed states.

Action Taken When the DTC Sets

* DTC P0571 is a Type A DTC.
* The TCM defaults the brake switch to OFF.
* The TCM disables grade braking.

Conditions for Clearing the DTC

DTC P0571 is a Type A DTC.

Diagnostic Aids

You have to drive the vehicle to experience a condition.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Allison - Automatic Transmission)
Connector End View Reference

* Component Connector End Views (Connector End Views By Name)
* Inline Harness Connector End Views (Connector End Views By Number)

Description and Operation

* Transmission General Description (Transmission General Description)
* Transmission Component and System Description (Transmission Component and System Description)
* Electronic Component Description (Electronic Component Description)

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Control Module References)for scan tool information

Circuit/System Verification

1. Diagnose all other BCM DTCs prior to DTC P0571. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).
2. Ignition ON, verify the TCM Service Brake Status Inverted changes between enabled and disabled when the brake pedal is depressed and released.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed on the Freeze Frame/Failure Records data.

Circuit/System Testing

Note: You must perform the Circuit/System Verification first.

1. Ignition ON, verify the stop lamp lights are ON when the brake pedal is depressed, and OFF when the brake pedal is released.

• If not the expected results, refer to Stop Lamps Malfunction (Stop Lamps Malfunction).

2. Verify the BCM Stop Lamp Relay Command parameter changes from OFF to ON when the brake pedal is depressed.

• If not the expected results, refer to Stop Lamps Malfunction (Stop Lamps Malfunction).

3. Verify the TCM Service Brake Status Inverted parameter changes between enabled and disabled when the brake pedal is depressed and released.
4. If there are no other BCM DTCs, diagnosis is accomplished by looking for an intermittent CAN circuit fault. Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device (Scan Tool Does Not Communicate with High Speed GMLAN Device).

Repair Instructions

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

Control Module References (Control Module References)for TCM replacement, setup, and programming

Repair Verification

If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) and perform the appropriate diagnostic procedure.