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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 Sierra Denali 🢒 Transmission 🢒 Automatic Transmission - Allison 🢒 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

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.
    • Ignition and battery voltage is between 9-18 V.

Conditions for Setting the DTC

This DTC sets when the TCM internal temperature is greater than 140°C (284°F) for 10 seconds.

Action Taken When the DTC Sets
    • The TCM does not request the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL).
    • DTC P0634 is stored in TCM history.
    • 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 damage 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

Connector End View Reference

Component Connector End Views

Description and Operation

    •  Transmission General Description
    •  Transmission Component and System Description
    •  Electronic Component Description

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
  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 a road test while observing the TCM Temperature parameter with a scan tool. The TCM Temperature parameter should rise and then stabilize.
  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.

Circuit/System Testing

    Note: You must perform the Circuit/System Verification first.

  1. Replace the TCM. Refer to Control Module References for TCM replacement, setup, and programming.
  2. Perform fast learn procedure. Refer to FastLearn Procedure.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References for TCM replacement, setup, and programming
    •  FastLearn Procedure

Repair Verification

If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.