DTC P0634. Chevrolet Tahoe

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2009 🢒 Tahoe - 2WD 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 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

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 ignition voltage is 11-18 volts.

•	The TCM temperature is -50°C (-58°F) to 146°C (295°F) for 5 seconds.

Conditions for Setting the DTC

•	The TCM has detected an internal overtemperature condition greater than 141°C (286°F) for 2 seconds.

•	The ignition voltage is greater than 18 volts and the TCM temperature is greater than 50°C (122°F).

Action Taken When the DTC Sets

•	DTC P0634 is a Type A DTC.

•	The TCM shifts to a default gear 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

Connector End View Reference

Component Connector End Views

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Circuit/System Verification

Start the Engine and check for DTC P0634.

Circuit/System Testing

Start the engine.
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.

Operate the vehicle under the same conditions as found in Failure Records and observe the TCM Temperature parameter on the scan tool.
Recheck for DTCs.

⇒	If the DTC resets, and the TCM 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 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 procedure.

•	Line Pressure Check procedure.

•	Control Solenoid Valve and Transmission Control Module Assembly Inspection .

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for control solenoid (w/body and TCM) valve assembly replacement, setup, and programming.