Allison - Automatic Transmission

DTC P0634

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 P0634
- Transmission Control Module (TCM) Overtemperature

Circuit/System Description

A thermistor is imbedded in the transmission control module (TCM). There are no external circuits. The TCM monitors the temperature and will take action to prevent damage to the TCM.

Conditions for Running the DTC

* Engine speed is greater than 200 RPM for 5 seconds.
* Battery voltage is between 9-18 V.

Conditions for Setting the DTC

The TCM detects the internal TCM temperature is 140°C (284°F) or greater for 10 seconds.

Action Taken When the DTC Sets

* DTC P0634 is a Type C DTC.
* The TCM shuts down and all power is removed from the solenoids.
* The transmission goes to a hydraulic default mode and will operate in reverse, neutral, and first, third, or fifth range.

Conditions for Clearing the DTC

DTC P0634 is a Type C DTC.

Diagnostic Aids

* Inspect the mounting of the TCM and for damaged or missing heat shields.
* You may have to drive the vehicle in order 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. Prior to cold start, Ignition ON, observe the TCM Temperature parameter with a scan tool. The TCM Temperature parameter should be approximately the same as the ambient temperature.
2. Perform the Road Test (Allison - Automatic Transmission) while observing the TCM Temperature parameter with a scan tool. The TCM Temperature parameter should rise and then stabilize.

• If the DTC resets, replace the TCM. Refer to Transmission Control Module Replacement (Allison - Automatic Transmission).

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.

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.