Restore Smooth Shifting to Your 2006 Trailblazer EXT
If you’re dealing with the headaches of a failing transmission control module—like harsh shifting, getting stuck in gear, or a persistent check engine light—you know how frustrating it can be. As a technician with over two decades of experience, I’ve seen countless GM vehicles, including the Trailblazer, suffer from these exact issues. The problem often isn’t the transmission itself, but the electronic brain that controls it. This T42 Transmission Control Module (TCM), part number 24238856, is the reliable, straightforward solution you need. It arrives pre-programmed to your vehicle’s specific VIN, eliminating the need for an expensive trip to the dealership for programming. It’s designed to restore the precise, smooth performance your vehicle had when it was new.
A Technician’s Notebook: The Misleading Limp Mode
A customer brought in a 2006 Trailblazer EXT stuck in what he called “permanent limp mode.” It wouldn’t shift past 2nd gear, and the dash was lit up. His previous mechanic quoted him for a full transmission rebuild, costing thousands. I hooked up my scan tool and saw a generic P0700 code, but also a few intermittent solenoid communication errors. Instead of tearing down the transmission, I checked the TCM. After 20 years in the bay, you learn that electrical faults often mimic major mechanical failures. We swapped in a VIN-programmed T42 module, and within 30 minutes, the truck was shifting perfectly through all gears. This is a prime example of how the right part, like this 2006 Trailblazer EXT TCM, can save you from a costly and unnecessary repair.
Is Your Trailblazer Exhibiting These Transmission Woes?
A failing TCM can manifest in several ways. If you’re experiencing any of the following, this module is likely the solution you need:
- ✔ Erratic, hard, or delayed gear shifts that make driving uncomfortable.
- ✔ The vehicle is stuck in a single gear (often called “limp mode”) to protect the transmission.
- ✔ A lit Check Engine Light or Transmission Warning Light, often with Diagnostic Trouble Codes (DTCs) like P0700, P0750, P0753, or other solenoid-related faults.
- ✔ Complete failure to upshift or downshift, leading to poor acceleration and terrible fuel economy.
- ✔ Intermittent loss of communication with the module, causing unpredictable performance.
Your Step-by-Step Guide to a Quick Installation
One of the best features of this part is its simple, plug-and-play installation. No special tools are needed, and most DIYers can complete the job in under 30 minutes. Here’s a basic guide:
- Safety First: Always disconnect the negative terminal from your vehicle’s battery before starting any electrical work. This prevents short circuits and helps reset the vehicle’s electronic systems.
- Locate the Module: On your 2006 Trailblazer EXT, the TCM is typically found in the engine compartment on the left-hand (driver’s) side. Check near the firewall or strut tower.
- Remove the Old Unit: Carefully unplug the electrical connectors. Press the release tabs firmly to avoid damaging the clips. Then, unbolt the module from its mounting bracket.
- Install the New Module: Mount the new, pre-programmed TCM in the same location and securely fasten the bolts. Reconnect the electrical connectors, ensuring they click into place.
- Final Steps: Reconnect the battery terminal. While the module is pre-programmed, it’s good practice to use a basic OBD-II scan tool to clear any stored fault codes from the vehicle’s memory. Start the engine and take it for a test drive to confirm smooth shifting.
Verified Vehicle Compatibility
This T42 TCM is a direct replacement for your 2006 Trailblazer EXT with an 8-cylinder engine. It is also compatible with a wide range of other General Motors vehicles from 2006-2014 that use the 4L60E, 4L65E, 4L70E, or 4L80E automatic transmissions. It is interchangeable with numerous part numbers, including 24242391, 24234503, 24252114, and 24238856. Please see the detailed fitment list below to ensure it matches your specific model.
TRAILBLAZER EXT 06 Transmission; (LH engine compartment), (8 cylinder)
ALLURE 06-09 Transmission; (lower air cleaner housing)
AVALANCHE 1500 07-08 Transmission; (next to battery)
CANYON 08-12 Transmission; (RH rear engine compartment)
COBALT 06-10 Transmission; (LH strut tower)
COLORADO 08-12 Transmission; (RH rear engine compartment)
DTS 06-11 Transmission; (RH front engine compartment)
ENVOY 06-09 Transmission; (LH engine compartment)
EXPRESS VANS 06-14 Transmission; (RH engine compartment)
G5/G6 06-10 Transmission; (LH strut tower)
GRAND PRIX 06-08 Transmission; (lower air cleaner housing)
HHR 06-11 Transmission; (LH engine compartment)
HUMMER H3 08-10 Transmission; (RH rear engine compartment)
IMPALA 06-11 Transmission; (lower air cleaner housing)
…and many more GM models. Verify your vehicle in the fitment chart.
Frequently Asked Questions
What exactly does a Transmission Control Module (TCM) do?
The TCM is the dedicated computer for your automatic transmission. It receives data from various sensors (like vehicle speed and engine RPM) to control shift points, torque converter lockup, and line pressure. A faulty one leads to poor shifting and performance.
Is this part really plug-and-play? What does VIN programming mean?
Yes. VIN programming means we load the latest GM-certified software specific to your vehicle’s Vehicle Identification Number (VIN) onto the module before shipping it. This ensures it communicates perfectly with your vehicle’s other computers right out of the box, with no dealer programming required.
Do I need to send my old TCM back (core charge)?
No, there is no core charge for this part. You can keep your old module or dispose of it, making the process hassle-free.
Will this fix a P0700 trouble code?
A P0700 code is a general fault code indicating the TCM has detected a problem. While this module often resolves the root cause (like internal failure or solenoid driver issues), it’s essential to ensure the transmission wiring and solenoids are in good condition. In many cases I’ve diagnosed, a new TCM is the final fix.
What if I have questions during installation?
We provide expert support to help you through the process. Our team understands these vehicles and parts, and we’re here to ensure your repair is successful.