Restore Flawless Shifting to Your 2006 Trailblazer EXT
If you’re dealing with the frustration of a transmission that won’t shift correctly, gets stuck in gear, or causes a check engine light, you’re not alone. The Transmission Control Module (TCM) is the brain of your automatic transmission, and when it fails, it can cause a host of drivability issues. This T42 series TCM is a direct-fit, reliable solution for your 2006 Trailblazer EXT, arriving pre-programmed to your vehicle’s VIN. This means you can skip the expensive trip to the dealership for programming and get your SUV back to performing as it should, with smooth, predictable gear changes.
A Technician’s Notebook
I remember a 2006 Trailblazer EXT that came into the shop with a really tricky intermittent issue. The owner complained of random harsh downshifts and occasional failure to shift out of 2nd gear, but no consistent trouble codes other than a general P0700. We checked the fluid, solenoids, and wiring harness—all looked fine. After hours of diagnostics, we finally traced the issue to the TCM. Heat soak was causing internal components to fail unpredictably. Installing a new, pre-programmed 2006 Trailblazer EXT TCM like this one solved the problem instantly. It’s a reminder that sometimes the computer itself is the root cause, not the mechanical parts it controls.
Is Your Trailblazer Showing These Telltale Signs of TCM Failure?
A faulty TCM can manifest in several ways. If you’re experiencing any of the following, this module is likely the solution you need. In my 20+ years of experience, these are the most common indicators I see in the shop for a failing GM transmission computer.
- ✔ Harsh, slamming, or erratic gear shifts.
- ✔ The vehicle is stuck in “limp mode” (usually 2nd or 3rd gear).
- ✔ Check Engine Light or Transmission Warning Light is illuminated with codes like P0700, P0750, P0753, P0758, or other solenoid-related faults.
- ✔ Delayed engagement when shifting from Park to Drive or Reverse.
- ✔ Complete loss of shifting capability or communication with the module.
- ✔ Noticeable decrease in fuel economy due to inefficient shifting.
Your Step-by-Step Installation Roadmap
This is a repair many DIY enthusiasts can handle with basic tools. For the 2006 Trailblazer EXT, the TCM is typically located in the left-hand (driver’s side) engine compartment, making access straightforward. The entire process should take less than an hour.
- Safety First: Disconnect the negative terminal from your vehicle’s battery to prevent any electrical shorts and to help reset the system.
- Locate the Module: Find the TCM in the LH engine compartment. It’s a silver box with electrical connectors.
- Disconnect and Remove: Carefully unplug the electrical harnesses. Then, unbolt the module from its mounting bracket.
- Install the New TCM: Mount the new module securely onto the bracket and reconnect the electrical harnesses. Ensure they click into place firmly.
- Reconnect Power: Re-attach the negative battery terminal.
- Final Clearing: While not always necessary, it’s good practice to use a basic OBD-II scan tool to clear any stored diagnostic trouble codes (DTCs) from the vehicle’s memory.
Verified Vehicle Compatibility
This module, part number 24238856, is a direct replacement for a wide range of General Motors vehicles equipped with the T42 TCM. While this page is focused on the 2006 Trailblazer EXT TCM, it also fits the models listed below. Always confirm your part number for a perfect match.
This part will fit these makes and models with these options:
- TRAILBLAZER EXT 06 Transmission; (LH engine compartment), (8 cylinder)
- TRAILBLAZER 06-09 Transmission; (LH engine compartment), (8 cylinder or SS)
- ENVOY & ENVOY XL 06-09 Transmission; (LH engine compartment), (8 cylinder)
- SILVERADO & SIERRA 1500/2500/3500 06-13 Transmission; (various locations, often next to battery)
- TAHOE, SUBURBAN, YUKON, AVALANCHE 07-09 Transmission; (next to battery)
- IMPALA & MONTE CARLO 06-11 Transmission; (lower air cleaner housing)
- COBALT, G5, G6, ION 06-10 Transmission; (LH strut tower)
- HUMMER H3 08-10 Transmission; (RH rear engine compartment)
- …and many more GM models from 2006-2014. Please verify fitment using your vehicle’s information.
Frequently Asked Questions
Do I need to get this programmed by a dealer?
No. This module comes fully pre-programmed to your vehicle’s specific VIN. It is a true plug-and-play solution, saving you time and money.
What is the primary function of this 2006 Trailblazer EXT TCM?
It controls all major functions of your automatic transmission, including shift points, shift pressure, and torque converter lockup, to ensure smooth operation and optimal fuel efficiency.
Is there a core charge for this part?
No, there is no core charge. You can keep your old part without needing to send it back, simplifying the repair process for you.
Will this fix a P0700 code?
A P0700 code is a general fault code indicating the TCM has detected a problem. While this module often resolves the root cause of a P0700, you should always diagnose any other specific codes (like for solenoids) that are present alongside it.
What kind of warranty is included?
This transmission control module is backed by our standard one-year warranty, giving you confidence and peace of mind in your repair.