M99 - Automatic Transmission
DTC P0634
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0634
- Transmission Control Module (TCM) Overtemperature
Circuit/System Description
The transmission control module (TCM) has a built-in temperature sensor to detect possible over-temperature conditions of the TCM. This fault indicates the TCM is in an overtemperature condition and the TCM has shut down to protect from possible heat damage. The TCM will remain off until the over temperature condition no longer exists. The TCM is part of the control solenoid (w/body and TCM) valve assembly and is not serviced separately.
Conditions for Running the DTC
* The engine is running.
* The TCM temperature is less than 150°C (302°F) for greater than 5 seconds.
* DTC P0634 is not set.
Conditions for Setting the DTC
The TCM has detected an internal overtemperature condition greater than 141°C (286°F) for 10 seconds.
Action Taken When the DTC Sets
* DTC P0634 is a Type A DTC.
* The TCM shifts to a default gear, shuts down, and turns OFF.
Conditions for Clearing the DTC
DTC P0634 is a Type A DTC.
Diagnostic Aids
Inspect the transmission cooler, transmission fluid lines, engine cooling system, and transmission fluid level, and inspect for any obstructions in the cooling system airflow which may cause an overheat condition. Inquire about customer towing or extreme driving conditions. An engine cooling system or transmission cooling system malfunction may cause this diagnostic to set. Perform the control solenoid (w/body and TCM) valve assembly inspection procedure before replacing the control solenoid (w/body and TCM) valve assembly.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views
Electrical Information Reference
* Circuit Testing
* Connector Repairs
* Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs
* High Voltage Disabling
* High Voltage Enabling
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Circuit/System Verification
Start the Engine and check for DTC P0634.
Circuit/System Testing
1. Start the engine.
2. Observe the transmission fluid temperature (TFT) and the engine coolant temperature (ECT). Ensure there are no current overheat conditions present in these systems.
• If an overheating concern is found, diagnose and repair that system first.
3. Operate the vehicle under the same conditions as found in Failure Records and observe the TCM Temperature parameter on the scan tool.
4. Recheck for DTCs.
• If the DTC resets, and the TCM power-up temperature sensor is not over 130°C (266°F), and the TFT is less than 120°C (248°F), replace the control solenoid (w/body and TCM) valve assembly.
• If the TCM power-up temperature sensor is over 130°C (266°F), inspect and repair the transmission cooler, transmission cooler fluid lines, engine cooling system, and transmission fluid level, and inspect for any obstructions in the cooling system airflow which may cause an overheat condition.
Component Testing
* Transmission Fluid Check (Transmission Fluid Check) procedure.
* Line Pressure Check (Line Pressure Check) procedure.
* Control Solenoid Valve and Transmission Control Module Assembly Inspection (Control Solenoid Valve and TCM Assembly Solenoid Performance Test) .
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control solenoid (w/body and TCM) valve assembly replacement. Refer to Control Module References for replacement, setup, and programming.