Is Your Trailblazer Running Rough? Get the Definitive Fix.
If you’re dealing with a frustrating no-start condition, a persistent Check Engine Light, or erratic engine behavior in your 2009 Chevrolet Trailblazer, the Engine Control Module (ECM) is a very likely culprit. As a technician with over two decades of experience under the hood, I’ve seen firsthand how a failing ECM can cause a cascade of confusing problems that seem impossible to pin down. This isn’t just a part; it’s the brain of your engine, and when it falters, everything from fuel economy to transmission shifting can suffer. This replacement 2009 Trailblazer Engine Control Module is the reliable, straightforward solution to restore your vehicle’s performance and peace of mind.
We take the guesswork and extra expense out of the repair. Before this module ever leaves our facility, we program it specifically for your vehicle using the VIN you provide at checkout. This means it arrives loaded with the latest GM software updates, ready for installation without a costly trip to the dealership. It’s a direct-fit replacement for part number 12678512 and a wide range of other GM service numbers, ensuring a perfect match and seamless integration.
Case Study: A Tricky Diagnosis
I remember a 2009 Trailblazer SS with the 6.0L that came into my shop with a complaint of intermittent stalling at stoplights and a weird, delayed shift from 2nd to 3rd gear. The owner had already replaced the throttle body and a transmission solenoid based on another shop’s advice, with no improvement. We scanned it and found no hard codes, just a history of a generic communication error (U0100). After checking all the primary wiring and grounds, we focused on the ECM. On the surface, it seemed fine, but a deep data stream analysis showed inconsistent voltage readings to the transmission control module. We swapped in a pre-programmed ECM like this one, and the problems vanished instantly. It’s a classic example of how a failing ECM can send you chasing ghosts—this part was the direct fix.
Common Signs of a Failing ECM
- ✔ Engine misfires, stalling, or difficulty starting.
- ✔ The Check Engine Light is illuminated, often with internal processor codes like P0601, P0602, or P0606.
- ✔ Poor or erratic automatic transmission shifting.
- ✔ A noticeable drop in fuel efficiency.
- ✔ Communication errors with other vehicle modules (U-codes).
- ✔ The engine runs in a reduced power or “limp” mode.
A Straightforward Guide to Installation
Replacing your 2009 Trailblazer Engine Control Module is a manageable job for a confident DIYer. Because we program it for you, the most complex step is already handled. Follow these general steps for a successful installation.
- Safety First: Always disconnect the negative terminal from your vehicle’s battery and wait at least 15 minutes for the system capacitors to discharge before you begin.
- Locate the ECM: On the 2009 Trailblazer, the ECM is typically found in the engine bay on the driver’s side, mounted to the engine itself or the inner fender.
- Disconnect Connectors: Carefully release the locking tabs on the wiring harness connectors and pull them straight out from the module. Never force them. Inspect the pins for any corrosion or damage.
- Remove the Old Module: Unbolt the old ECM from its mounting bracket. Keep the hardware, as you may need to reuse it.
- Install the New Module: Mount your new, pre-programmed ECM securely onto the bracket.
- Reconnect and Secure: Firmly plug the wiring harnesses back into the new module until they click into place. Reconnect the negative battery terminal.
- Perform Relearn (If Necessary): While not always required, you may need to perform a security relearn procedure (often called a Passlock or Passkey relearn), which typically involves cycling the key in the ignition. Consult your vehicle’s service information for specific steps.
Will This Fit My Vehicle?
This ECM is a guaranteed fit for a wide array of GM vehicles. While this listing is focused on the 2009 Trailblazer Engine Control Module, it is also the correct, pre-programmed solution for the following models. Please verify your vehicle and engine options below.
TRAILBLAZER 09 Electronic Control Module; (LH engine), 6.0L
ENVOY 09 Electronic Control Module; (LH engine), 5.3L
SAAB 9-7X 09 Electronic Control Module; (LH engine)
HUMMER H3 09-10 Electronic Control Module; (RH firewall)
COLORADO 09-12 Electronic Control Module; (RH firewall)
CANYON 09-12 Electronic Control Module; (RH firewall)
CORVETTE 09 Electronic Control Module; (RH engine compartment), ZR1
CTS 09 Electronic Control Module; (RH front engine compartment), 6.2L
DTS 09-11 Electronic Control Module
LUCERNE 09-11 Electronic Control Module; (lower part of air cleaner box), 4.6L
SRX 09 Electronic Control Module; (LH engine compartment), (4.6L)
STS 09-10 Electronic Control Module; (LH frame rail), 4.4L or 4.6L
XLR 09 Electronic Control Module; (RH front engine compartment)
Interchangeable Service Numbers: 12636659, 12639300, 1263605, 12628993, 12628911, 12625453, 12622175, 12630464, 12678512
Frequently Asked Questions
Do I need to do anything after installation?
Since we program the module to your VIN, it’s typically a plug-and-play installation. In some cases, a security relearn procedure may be necessary, which can be done without special tools. We recommend checking your vehicle’s specific procedure.
How do I provide my VIN?
Simply enter your vehicle’s 17-digit VIN in the designated field during the checkout process. This is crucial for us to program the module correctly for your vehicle’s specific configuration.
Is this a new or used part?
This is a high-quality, tested replacement part that is guaranteed to function to OEM specifications. We ensure every module is ready for reliable, long-term service.
What if my original part number is not 12678512?
That’s okay. This ECM is a direct replacement for all the service numbers listed in the description (e.g., 12636659, 12628993, etc.). As long as your vehicle is on the compatibility list, this module will work.
Will this fix my transmission problems?
The ECM plays a critical role in controlling transmission functions. If your shifting problems are caused by faulty signals from the engine computer, then yes, this module can resolve them. However, it will not fix internal mechanical failures within the transmission itself.
What is the warranty on this part?
This module comes with our standard warranty, ensuring it is free from defects in function. Please see our warranty page for full details and terms.