Restore Smooth Shifting to Your GMC Envoy
If you’re dealing with the frustration of a GMC Envoy that shifts harshly, gets stuck in gear, or throws transmission-related check engine light codes, you’ve come to the right place. As a technician with over two decades of experience, I’ve seen countless drivers worry about a complete transmission failure when the real culprit is a faulty Transmission Control Module (TCM). This T42 TCM, part number 24255280, is the definitive solution for your 2006-2009 GMC Envoy and a wide range of other GM vehicles, designed to restore factory performance and reliability without a costly trip to the dealership.
The TCM is the brain of your automatic transmission. It processes data from various sensors to control shift points, torque converter clutch engagement, and line pressure. When it fails, communication breaks down, leading to the unpredictable and often jarring performance you’re experiencing. Our modules solve this by arriving at your door pre-programmed to your vehicle’s specific VIN. This crucial step ensures that the module communicates flawlessly with your vehicle’s other computers, like the Engine Control Module (ECM), right out of the box. You get a plug-and-play fix that eliminates the need for expensive dealer-only programming tools.
Case Study: The Envoy That Dodged a Rebuild
A customer brought in their 2008 Envoy, convinced they needed a new transmission. It was banging into gear and was stuck in what we call ‘limp mode’—third gear only. The quote from another shop was over $3,000 for a transmission rebuild. I hooked up my scan tool and saw a classic set of codes: P0700 (Transmission Control System Malfunction) and a few solenoid circuit codes. Instead of tearing down the transmission, I checked the TCM. After seeing no physical damage, my experience pointed to internal electronic failure, a common issue in these T42 modules after years of heat cycles. We replaced it with one of our VIN-programmed TCMs. The total repair time was under an hour, and the cost was a fraction of the rebuild quote. The customer drove away with a perfectly shifting vehicle, saving thousands. This is a perfect example of how correctly diagnosing the electronics first can save you a massive headache and expense.
Is Your Envoy’s Transmission Acting Up?
A failing TCM can manifest in several ways. If you notice any of the following, it’s a strong indicator that your transmission control module needs attention. Addressing it early can prevent further damage to your transmission’s mechanical components.
- ✔ Harsh, erratic, or delayed gear shifts.
- ✔ The vehicle is stuck in a single gear (limp mode).
- ✔ Check Engine Light or Transmission Warning Light is illuminated.
- ✔ Diagnostic Trouble Codes (DTCs) are present, such as P0700, P0750, P0753, P0758, or other solenoid-related faults.
- ✔ Poor fuel economy and a feeling of lost power.
- ✔ Complete loss of communication with the TCM (no-start or no-shift condition).
A Straightforward Guide to Installation
One of the best parts about this solution is how accessible it is for a DIY mechanic. You don’t need a vehicle lift or specialized transmission tools. For a 2006-2009 Envoy TCM, the module is typically located in the engine compartment for easy access.
- Safety First: Disconnect the negative terminal from your vehicle’s battery to prevent any electrical shorts and to help reset the vehicle’s computer systems.
- Locate the TCM: On the GMC Envoy and related platforms (like the Trailblazer or Saab 9-7X), the TCM is found in the left-hand (driver’s side) of the engine compartment.
- Disconnect and Remove: Carefully unplug the electrical connectors. They have locking tabs that may need to be gently pried up. Once disconnected, unbolt the module from its mounting bracket.
- Install the New Module: Bolt the new, pre-programmed TCM into place and securely reconnect the electrical harnesses. Ensure they click into place.
- Final Steps: Reconnect the battery terminal. Start the vehicle and let it idle for a few minutes. While the programming is already done, it’s good practice to use a basic OBD2 scan tool to clear any stored fault codes from the system. Take the vehicle for a test drive to confirm smooth shifting.
Verified Fitment for Your GM Vehicle
This T42 TCM is a direct replacement for part number 24255280 and is interchangeable with many other service numbers. It fits a wide array of GM cars, trucks, and SUVs equipped with 4-speed automatic transmissions like the 4L60E, 4L65E, and 4L70E. Please verify your model and year from the list below.
This part is confirmed to fit:
- GMC Envoy / Envoy XL / Trailblazer / Trailblazer EXT: 2006-2009 (8-cylinder models, LH engine compartment)
- Chevrolet Silverado / GMC Sierra 1500: 2007-2013 (Located next to the battery)
- Chevrolet Tahoe / Suburban / GMC Yukon: 2007-2009 (Located next to the battery)
- Chevrolet Colorado / GMC Canyon: 2008-2012 (RH rear engine compartment)
- Chevrolet Impala / Monte Carlo: 2006-2011 (Under lower air cleaner housing)
- Buick LaCrosse / Allure: 2006-2009 (Under lower air cleaner housing)
- Pontiac G6 / Grand Prix: 2006-2010 (LH strut tower)
- Hummer H3: 2008-2010 (RH rear engine compartment)
- Saab 9-7X: 2006-2009 (LH engine compartment)
- …and many more models including Savana/Express vans, Cobalt, HHR, Saturn Vue, and Cadillac DTS.