Restore Peak Performance to Your HUMMER H3
Is your 2009-2010 HUMMER H3 suffering from frustrating and unpredictable engine problems? Issues like stalling, a persistent check engine light, or a complete no-start condition can often be traced back to a failing Engine Control Module (ECM). As the brain of your vehicle’s engine management system, a faulty ECM can cause chaos. This replacement ECM, part number 12678512, is the definitive solution to get your rugged H3 running smoothly and reliably again.
With over 20 years of experience in automotive diagnostics, I’ve seen firsthand how a failing computer can mimic other problems, leading to wasted time and money on unnecessary parts. This is why we offer a comprehensive solution. Before this module ships, we flash it with the latest official GM software updates, specifically programmed to your vehicle’s unique VIN. This critical step ensures seamless communication with your H3’s other systems, eliminating the need for an expensive trip to the dealership for programming.
From the Diagnostic Bay: The Intermittent H3 Stall
A customer brought in their 2009 H3 with a problem that had stumped two other shops: it would randomly stall at stoplights, but only after it was fully warmed up. There were no consistent trouble codes, just a history of random communication faults. We could have chased our tails replacing sensors, but experience pointed to the ECM. Heat soak was causing an internal failure in the module’s processor. We installed a VIN-programmed 2009-2010 HUMMER H3 ECM, performed a quick crankshaft position relearn, and the problem was solved for good. It’s a classic case where the right part, correctly prepared, makes all the difference.
Common Signs of a Failing Engine Computer
If your vehicle is experiencing any of the following, a faulty ECM could be the culprit. Replacing it can be the most direct path to a reliable repair.
- ✔ Check Engine Light is on with codes for internal processor failure (e.g., P0601, P0606).
- ✔ Vehicle refuses to start or has a hard starting condition.
- ✔ Unexplained stalling or rough idling.
- ✔ Poor fuel economy and engine performance.
- ✔ Communication issues with scan tools or other modules (U-series codes).
- ✔ Erratic automatic transmission shifting.
A Straightforward Guide to Installation
Installing your new 2009-2010 HUMMER H3 ECM is a manageable job for a DIYer with basic tools. On the H3, the ECM is conveniently located on the right-hand (passenger side) firewall in the engine bay.
- Safety First: Always disconnect the negative terminal from your vehicle’s battery and wait 10-15 minutes for the system capacitors to discharge.
- Locate the ECM: Open the hood and find the module on the passenger-side firewall. It will have several large electrical connectors attached.
- Disconnect Connectors: Carefully release the locking tabs on each wiring harness connector and pull them straight out. Avoid pulling on the wires themselves.
- Remove the Module: Unbolt the old ECM from its mounting bracket. Keep the hardware, as you will need it for the new module.
- Install the New ECM: Mount the new, pre-programmed module in place using the original hardware. Reconnect the wiring harnesses, ensuring they click securely into place.
- Reconnect Battery: Reattach the negative battery terminal.
- Final Steps: In many cases, a Crankshaft Position System Variation (CASE) relearn procedure may be required using a capable scan tool to prevent a P1336 trouble code. Some vehicles may also require a security relearn, which typically involves a simple key-cycling procedure.
Verified Vehicle Compatibility
This ECM is a direct replacement for service number 12678512 and is interchangeable with 12636659, 12639300, 1263605, 12628993, 12628911, 12625453, 12622175, and 12630464. It is guaranteed to fit the following vehicles:
- HUMMER H3: 2009-2010
- Chevrolet Colorado: 2009-2012 (2.9L, 3.7L)
- GMC Canyon: 2009-2012 (2.9L, 3.7L)
- Chevrolet Trailblazer: 2009 (6.0L)
- GMC Envoy: 2009 (5.3L)
- Saab 9-7X: 2009
- 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 Corvette: 2009 (ZR1)
- Buick Lucerne: 2009-2011 (4.6L)
This professionally prepared 2009-2010 HUMMER H3 ECM is your solution for a lasting and reliable repair.
Frequently Asked Questions
Why do you need my VIN?
Your Vehicle Identification Number (VIN) allows us to program the ECM with the exact software and calibrations for your HUMMER H3’s specific options, engine, and transmission. This ensures it works perfectly right out of the box.
Is this a simple plug-and-play installation?
Yes, for the most part. Because we pre-program the module, you avoid a trip to the dealer. However, some GM vehicles may require a simple security relearn (key cycle procedure) or a CASE relearn (with a scan tool) to be fully operational and clear all codes.
Will this fix my check engine light?
If the check engine light is caused by an internal ECM failure (like code P0601), then yes, this part will resolve the issue. It’s crucial to properly diagnose the vehicle first to ensure the ECM is the root cause.
What if I have a different part number on my old module?
This module, 12678512, is the latest service replacement for many older part numbers. As long as your vehicle is on our compatibility list and your old part number is one of the listed interchanges, this module will work correctly.
Do I need any special tools for the installation?
You will only need basic hand tools like a socket set to remove the module from its bracket. A capable bi-directional scan tool is recommended for performing a CASE relearn if needed, but the physical installation is very straightforward.