Restore Peak Performance to Your Hummer H3
Is your 2009-2010 Hummer H3 suffering from frustrating issues like stalling, poor fuel economy, a persistent check engine light, or a no-start condition? A failing Engine Control Module (ECM) is often the culprit behind these perplexing problems. As the brain of your vehicle’s engine management system, its proper function is critical. This direct-replacement ECM, part number 12636659, is the definitive solution to get your rugged H3 running smoothly and reliably again.
We take the guesswork and dealer expense out of the equation. Before this module ships, our experts will program it with the latest official GM software updates, specifically matched to your vehicle using the VIN you provide at checkout. This means the 2009-2010 Hummer H3 ECM arrives at your door ready for a straightforward installation, with no additional programming or security relearn procedures required. It’s the most efficient way to restore your vehicle’s factory-specified performance and clear those stubborn diagnostic trouble codes.
A Technician’s Notebook: The Hard-to-Trace Fault
I once had a 2009 H3 in the bay that was a real head-scratcher. The owner reported intermittent stalling at traffic lights and a random collection of communication codes (U-codes) along with a P0300 random misfire. We checked all the usual suspects: fuel pressure was solid, spark plugs were new, and the wiring harnesses looked pristine. After hours of diagnostics, we connected a scope to the main processor’s power and ground feeds at the ECM. We found a slight voltage drop inside the module itself whenever the engine warmed up. It was an internal failure of the ECM’s processor, something a standard scan tool can’t always pinpoint. Swapping in a pre-programmed ECM like this one resolved all issues instantly. These internal faults are more common than you’d think and can mimic a dozen other problems.
Common Signs of a Failing ECM
- ✔ Check Engine Light is illuminated with codes like P0601, P0606, or other processor faults.
- ✔ The engine cranks but will not start.
- ✔ Unexplained drops in fuel efficiency and poor engine performance.
- ✔ Intermittent stalling, hesitation, or rough idling.
- ✔ Automatic transmission shifting issues or harsh engagement.
- ✔ Communication errors with other vehicle modules (often showing U-codes).
- ✔ Apparent failure of multiple sensors at once.
A Straightforward Guide to Installation
Replacing the 2009-2010 Hummer H3 ECM is a job most DIYers can handle with basic tools. Since we program it for you, there are no complex computer steps involved.
- Safety First: Disconnect the negative terminal from your vehicle’s battery and secure it away from the post to prevent accidental reconnection.
- Locate the ECM: On the Hummer H3, the Engine Control Module is typically located on the right-hand (passenger) side of the firewall in the engine compartment.
- Disconnect Harnesses: Carefully release the locking tabs on the electrical connectors and pull them straight out from the module. Avoid pulling on the wires themselves. There may be two or three large connectors.
- Remove the Old Module: Unbolt the mounting hardware that secures the old ECM to the firewall. Keep the bolts and any brackets safe for reinstallation.
- Install the New Module: Mount your new, pre-programmed ECM in the same location using the original hardware. Ensure it is secure.
- Reconnect Everything: Firmly plug the electrical harnesses back into the new module until they click into place. Reconnect the negative battery terminal.
- Final Check: Turn the key to the ‘On’ position for 10-15 seconds before starting the engine. This allows the other modules to recognize the new ECM. Start your vehicle and enjoy restored performance.
Verified Vehicle Compatibility
This module is a direct replacement for service number 12636659 and is interchangeable with 12639300, 1263605, 12628993, 12628911, 12625453, 12622175, 12630464, and 12678512. It is guaranteed to fit the following vehicles:
- HUMMER H3: 2009, 2010 (3.7L)
- Cadillac CTS: 2009 (6.2L)
- Cadillac DTS: 2009-2011
- Cadillac SRX: 2009 (4.6L)
- Cadillac STS: 2009 (4.4L, 4.6L), 2010 (4.6L)
- Cadillac XLR: 2009
- Chevrolet Colorado: 2009, 2010-2012 (2.9L, 3.7L)
- Chevrolet Corvette: 2009 (ZR1)
- Chevrolet Trailblazer: 2009 (6.0L)
- GMC Canyon: 2009, 2010-2012 (2.9L, 3.7L)
- GMC Envoy: 2009 (5.3L)
- Buick Lucerne: 2009-2011 (4.6L)
- Saab 9-7x: 2009
Frequently Asked Questions About Your Hummer ECM
Do I need to program this 2009-2010 Hummer H3 ECM?
Do I need to program this 2009-2010 Hummer H3 ECM?
No. We handle all the programming for you before shipment. Simply provide your vehicle’s 17-digit VIN during checkout, and the module will arrive ready for installation with the latest GM software for your specific vehicle.
Where is the ECM located on my 2009 Hummer H3?
You will find the Engine Control Module mounted to the firewall on the passenger side of the engine compartment.
Why do you need my VIN?
The Vehicle Identification Number (VIN) allows us to flash the ECM with the exact software calibration file that General Motors specifies for your H3’s engine, transmission, and factory options. This ensures perfect compatibility and performance.
Will this part fix my check engine light?
If the check engine light is caused by an internal failure of the ECM (common codes include P0601 through P0606), then this replacement module will solve the problem. It is crucial to properly diagnose the vehicle first to ensure the ECM is the root cause.
Is this a simple plug-and-play installation?
Yes. Because the unit comes fully programmed to your VIN, the physical installation is a direct swap. No special tools or software are needed. Just bolt it in, plug in the connectors, and you’re ready to go.