Allison - Automatic Transmission

DTC P0703

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 P0703
- Brake Switch Circuit

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 is constantly monitoring the serial data sent from the BCM for the correct number and sequence of counts for the brake pedal switch status.

Conditions for Running the DTC

* Engine speed is greater than 200 RPM for 5 seconds.
* Ignition and battery voltage is between 9-18 V.
* The TCM is receiving the brake switch status message.

Conditions for Setting the DTC

The TCM detects an error in the rolling count value that does not match with the BCM count, 5 times within 10 seconds.

Action Taken When the DTC Sets

* DTC P0703 is a Type C DTC.
* The TCM defaults the brake switch status to OFF.

Conditions for Clearing the DTC

DTC P0703 is a Type C DTC.

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. DTC P0703 is an informational DTC. Diagnose all other body control module DTCs prior to DTC P0703. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).
2. If there are no other body control 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).
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 from the Freeze Frame/Failure Records data.

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
* FastLearn Procedure (Allison - Automatic Transmission)

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.