2005–2008 Chevrolet Silverado GMC Sierra Allison A40 TCM 25798264

Remanufactured Transmission Control Module

This listing is for a professionally remanufactured Allison A40 6-speed Transmission Control Module (TCM) for select 2005–2008 Chevrolet Silverado and GMC Sierra 2500/3500 trucks equipped with a 6.6L Duramax diesel engine.

Each module is inspected, remanufactured, and tested before shipping.

Vehicle Fitment

• 2005–2008 Chevrolet Silverado 2500

• 2005–2008 Chevrolet Silverado 3500

• 2005–2008 GMC Sierra 2500

• 2005–2008 GMC Sierra 3500

• 6.6L Duramax diesel engine

• Select LLY, LBZ, and LMM applications

• Allison 6-speed automatic transmission

• A40 Transmission Control Module

Fitment may vary by vehicle configuration and production date. Match your original module’s part number before ordering.

Compatible Part Number

• 25798264

Your original TCM part number must match 25798264. Compatibility cannot be confirmed using only the vehicle’s year, make, model, engine, or transmission.

Contact us before ordering if the original part number is missing, unreadable, or does not match.

What You Will Receive

• One remanufactured Allison A40 TCM

• Part number 25798264

• Module inspection and testing before shipment

• Installation-ready replacement module

Common TCM Failure Symptoms

A failing Transmission Control Module may be associated with:

• Check Engine light illuminated

• Transmission warning message

• Harsh, delayed, or erratic shifting

• Transmission remaining in one gear or fail-safe mode

• Delayed engagement into Drive or Reverse

• Loss of communication with the TCM

• Intermittent transmission operation

• Transmission-related diagnostic trouble codes

These symptoms do not independently confirm that the TCM is defective. Proper diagnosis is required before ordering.

Programming and Installation

Programming requirements may vary depending on the vehicle and how the replacement module is prepared.

Confirm the programming requirements before ordering. Do not assume the module is plug-and-play unless the listing option or order confirmation specifically states that programming is included.

Professional installation is strongly recommended. Vehicle-specific setup, programming, or relearning procedures may be required after installation.

Important Diagnostic Information

The customer or installing technician is responsible for confirming that the TCM is the source of the vehicle’s problem.

Before installing the replacement module, inspect:

• Transmission wiring and connectors

• Power and ground circuits

• Battery and charging-system voltage

• Communication circuits

• Transmission solenoids

• Related drivetrain components

Installing a replacement TCM without correcting an existing electrical or transmission problem may damage the replacement module.

Verify Before Ordering

Please confirm all of the following:

• The original part number is 25798264

• The vehicle has the correct Allison 6-speed transmission

• The module connectors and housing match

• The vehicle has been properly diagnosed

• Any programming requirements have been confirmed

Contact us before purchasing if you need assistance confirming compatibility.