Is Your HUMMER H3 Running Rough? The Engine Control Module Could Be the Culprit.
The Engine Control Module (ECM), often called the engine computer, is the electronic brain of your 2009-2010 HUMMER H3. It’s responsible for managing everything from fuel injection and ignition timing to emissions controls and transmission shifting. When this critical component begins to fail, it can cause a cascade of confusing and frustrating problems, leaving your rugged H3 feeling unreliable. Symptoms can range from a simple check engine light to a vehicle that won’t start at all. If you’re experiencing erratic engine behavior, poor fuel economy, or stalling, a faulty ECM is a likely cause.
The Direct-Fit Solution: A Pre-Programmed 2009-2010 HUMMER H3 ECM
Replacing an ECM isn’t just about swapping a box. Traditionally, a new module requires a trip to the dealership for expensive and time-consuming programming to sync it with your vehicle’s specific Vehicle Identification Number (VIN) and security systems. We eliminate that step entirely. This ECM, part number 12639300, arrives at your door fully programmed with the latest GM software updates, tailored specifically to your H3. Simply provide us with your VIN during checkout, and our technicians will handle the complex programming. This means you get a true plug-and-play solution, saving you hundreds of dollars in dealer fees and getting your Hummer back on the road faster.
From the Diagnostic Bay
We had a 2009 H3 come into the shop with a ghost of a problem. The owner complained of random stalling at traffic lights, but there were no consistent trouble codes. We checked the fuel pump, sensors, and wiring, but everything seemed fine. On a hunch, we monitored the ECM’s live data during a long test drive and finally saw it: the processor would momentarily drop communication, causing the engine to cut out. The original ECM was failing internally under specific thermal conditions. We replaced it with a VIN-programmed unit like this one, and the problem was solved instantly. The customer was thrilled to have their reliable H3 back without the guesswork and high cost of a dealership visit.
Common Symptoms of a Failing HUMMER H3 ECM
- ✔ Persistent Check Engine Light (CEL) that won’t clear or returns immediately.
- ✔ Engine stalling, stumbling, or hesitating, especially when warm.
- ✔ A complete no-start condition where the engine cranks but won’t fire up.
- ✔ Noticeable decrease in fuel efficiency.
- ✔ Poor engine performance, lack of power, or rough idling.
- ✔ Communication errors with diagnostic scan tools.
- ✔ Automatic transmission shifting erratically or harshly.
Guaranteed Compatibility and Simple Installation
This Engine Control Module is a direct replacement for a wide range of GM vehicles, but this listing is specifically for the 2009-2010 HUMMER H3 ECM. It is a direct replacement for multiple service numbers, including 12636659, 12639300, 1263605, 12628993, 12628911, 12625453, 12622175, 12630464, and 12678512. On your H3, the ECM is typically located on the right-hand side of the firewall in the engine bay. Installation is straightforward for a DIY mechanic: disconnect the battery, unplug the electrical connectors from the old module, unbolt it, and install the new one in its place. Reconnect the connectors and the battery, and you’re ready to go. No additional programming or security relearn procedures are necessary.
Frequently Asked Questions
Do I need to have this ECM programmed by a dealer?
No. This is the primary benefit of our service. We program the module to your vehicle’s specific VIN before we ship it. It arrives ready for installation with no extra programming required.
What is a VIN and why do you need it?
The VIN (Vehicle Identification Number) is a unique 17-digit code for your specific vehicle. We use it to load the correct GM-certified software, engine calibrations, and security information onto the ECM so it communicates perfectly with the other modules in your HUMMER H3.
Where is the ECM located on my 2009-2010 HUMMER H3?
The Engine Control Module on the 2009-2010 H3 is located in the engine compartment, mounted to the firewall on the right-hand (passenger) side.
Will this fix my check engine light?
If the check engine light is on due to an internal failure of the ECM, then yes, this part will resolve the issue. However, if the light is caused by a different faulty component (like an oxygen sensor or ignition coil), that part will still need to be addressed.
Is the installation difficult?
For someone with basic mechanical skills, the installation is straightforward. It involves disconnecting the vehicle’s battery, unplugging the wiring harnesses, and removing a few bolts. Since our module is pre-programmed, there are no complicated computer steps involved.
My original part number isn’t 12639300, but it’s on your list. Will this work?
Yes. GM often updates part numbers over time. The list of service numbers provided (12636659, 12628993, etc.) are all interchangeable. As long as your original part number is on our list, this module is the correct replacement for your vehicle.