Service Information

Volt

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 condition of the transmission control module. This temperature sensor is used to protect the TCM from heat damage due to an over temperature condition. The transmission control module is part of the control solenoid valve assembly and is not serviced separately.

Conditions for Running the DTC

•	The system voltage is 11-18V.

•	The TCM temperature is at least -50°C (-58°F) and no more than 146°C (295°F) for 5 seconds.

Conditions for Setting the DTC

•	The TCM temperature is greater than 141°C (286°F) for 2 seconds.

•	The system voltage is greater than 18 V and the transmission control module 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, inspect for any obstructions in the cooling system airflow which may cause an overheat condition. Enquire about any towing by the customer or extreme driving conditions. An engine cooling system or transmission cooling system malfunction may cause this diagnostic to set.

Reference Information

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

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Verify that DTC P0563 is not set.

⇒	If DTC is set, refer to DTC B1325, B1330, B1517, C0800, C0899, C0900, C12E1, C12E2, P0562, P0563, P1A0C, P1A0D, or P1EFC .

Vehicle ON, observe the scan tool Transmission Fluid Temperature parameter. The reading should be less than 141°C (286°F).

⇒	If greater than the specified range, test for a transmission overheat condition. Refer to Automatic Transmission Overheating .

Observe the scan tool TCM temperature parameter. The reading should be less than 141°C (286°F).

⇒	If greater than the specified range, replace the Q8 control solenoid assembly.

Component Testing

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 Valve Assembly and Transmission Control Module Assembly replacement, programming, and setup.