Is Your Hummer H3 Running Rough? The ECM Might Be the Culprit.
If your 2009-2010 Hummer H3 is experiencing baffling issues like a persistent check engine light, stalling, poor fuel mileage, or a complete no-start condition, the problem may lie with its electronic brain: the Engine Control Module (ECM). The ECM is the master computer responsible for managing everything from fuel injection and ignition timing to emissions controls and transmission communication. When it fails, it can cause a cascade of problems that are often difficult to diagnose, leading to frustrating and expensive trips to the mechanic.
This replacement Engine Control Module, part number 12678512, is the definitive solution to restore your vehicle’s performance and reliability. Unlike a generic part from a local store, this module is delivered to you fully programmed with the latest official GM software updates, specifically matched to your vehicle using its unique Vehicle Identification Number (VIN). This critical programming step ensures seamless integration, proper function of all systems, and a true plug-and-play installation experience, getting you back on the road faster.
From the Diagnostic Bay
We recently had a 2009 Hummer H3 come in that had its owner completely stumped. The vehicle would randomly stall at traffic lights and had an intermittent check engine light with a U0100 ‘Lost Communication with ECM/PCM’ code. The owner had already replaced the battery and checked all the main power and ground wires. After hooking up our professional scan tool, we noticed the ECM would occasionally drop offline entirely. Instead of a costly diagnostic session at the dealership followed by a new, unprogrammed module, we sourced this exact part. We provided the VIN, received the pre-programmed module two days later, and installed it in under 30 minutes. After a quick security relearn procedure, the H3 started right up and ran perfectly. The communication codes vanished, and the stalling issue was completely resolved, saving the customer hundreds of dollars and significant downtime.
Symptoms of a Failing Hummer H3 Engine Control Module
- ✔ Check Engine Light: The most common sign. You may see codes related to sensor failures, misfires, or internal computer errors.
- ✔ No-Start or Hard Starting: The ECM controls the fuel pump and ignition coils. If it fails, the engine may not get the fuel or spark it needs to start.
- ✔ Poor Engine Performance: Noticeable loss of power, hesitation during acceleration, rough idling, and engine misfires can all point to a faulty ECM.
- ✔ Decreased Fuel Economy: An ECM that isn’t correctly managing the air-fuel mixture will cause the engine to run inefficiently, burning more gasoline than necessary.
- ✔ Transmission Shifting Problems: The ECM works in tandem with the Transmission Control Module (TCM). A failing ECM can send incorrect data, leading to harsh shifts, delayed engagement, or the transmission getting stuck in one gear.
- ✔ Intermittent Stalling: The engine may suddenly shut off while driving or when coming to a stop, which can be a significant safety concern.
The Direct-Fit Solution: Your 2009-2010 Hummer H3 ECM
Don’t settle for a questionable part that requires expensive dealer programming. This module is a direct-fit replacement for your original unit and is guaranteed to be compatible. By providing your VIN during checkout, you ensure that the module you receive is loaded with the precise software calibration for your H3’s specific engine, transmission, and options. This eliminates compatibility guesswork and ensures all related vehicle systems function as intended from the moment of installation.
This module is a direct replacement for a wide range of GM service numbers, including: 12636659, 12639300, 1263605, 12628993, 12628911, 12625453, 12622175, 12630464, and 12678512. It also fits an extensive list of other GM vehicles, making it a proven and reliable component across the platform.
Complete Vehicle Compatibility List:
This part is verified to fit the following vehicles and configurations:
- Buick Lucerne (2009-2011) – 4.6L
- Cadillac CTS (2009) – 6.2L
- Cadillac DTS (2009-2011)
- Cadillac SRX (2009) – 4.6L
- Cadillac STS (2009-2010) – 4.4L, 4.6L
- Cadillac XLR (2009)
- Chevrolet Colorado (2009-2012) – 2.9L, 3.7L
- Chevrolet Corvette (2009) – ZR1
- Chevrolet Trailblazer (2009) – 6.0L
- GMC Canyon (2009-2012) – 2.9L, 3.7L
- GMC Envoy (2009) – 5.3L
- Hummer H3 (2009-2010) – 3.7L
- Saab 9-7x (2009)
Frequently Asked Questions
Do I need to get this ECM programmed by a dealer?
No. The main benefit of this part is that we handle all the programming for you before it ships. Simply provide your vehicle’s VIN when you place your order, and it will arrive ready to install with the latest GM software for your specific vehicle.
Is this a difficult part to install?
For most DIY mechanics, the installation is straightforward. It typically involves disconnecting the battery, unplugging the electrical connectors from the old ECM, unbolting it from its bracket (often on the firewall or inner fender), and then installing the new one in reverse order. While it is plug-and-play, some GM vehicles may require a simple security relearn procedure, which can usually be done without special tools. Instructions are widely available online.
Where do I find my vehicle’s VIN?
Your 17-digit Vehicle Identification Number (VIN) can be found on a metal plate on the driver’s side dashboard (visible through the windshield), on the driver’s side door jamb sticker, or on your vehicle’s registration and insurance documents.
Will this fix my check engine light?
If the check engine light is caused by a faulty ECM, then yes, this part will resolve the issue. However, the check engine light can be triggered by many other failing components (like sensors or solenoids). It is always recommended to have the trouble codes read by a scanner to help confirm that the ECM is the root cause of the problem.
What happens if I forget to provide my VIN?
The programming is essential for the part to work correctly. If you do not provide a VIN at checkout, our customer service team will contact you to retrieve it. We cannot ship the module until it has been programmed, as an unprogrammed unit will not function in your vehicle.