Is Your Hummer H3 Running Rough or Not Starting at All?
As a mechanic with two decades of diagnostic experience, I’ve seen countless H3s roll into the shop with baffling issues. One minute they run fine, the next they’re plagued with a persistent check engine light, erratic idling, stalling, or a complete no-start condition. Often, after hours of chasing down sensors and wiring, the root cause points directly to a failing Engine Control Module (ECM). The ECM is the brain of your vehicle, and when it malfunctions, it can create a cascade of frustrating and hard-to-diagnose problems.
The Dealership-Free Solution for Your 2009-2010 Hummer H3 ECM
Don’t let a faulty computer keep your rugged H3 sidelined. This is a direct-fit replacement Engine Control Module for your 2009-2010 Hummer H3. The best part? We handle the complicated part for you. Before we ship it, our technicians will program the module with the latest GM-certified software, specifically matched to your vehicle using the VIN you provide at checkout. This means it arrives at your door ready for a straightforward installation, saving you from an expensive tow and the high programming fees at a dealership.
Expert Pro Tip: Pre-Installation Connector Check
Before plugging in your new ECM, take a moment to closely inspect the vehicle’s harness connectors. Over time, moisture and dirt can cause subtle corrosion on the pins, leading to poor connections that can mimic ECM failure or even damage the new module. I recommend using a small brush and a quality electronic contact cleaner to gently scrub the pins. A tiny dab of dielectric grease on the connector seal can also help prevent future moisture intrusionโa common issue I’ve seen on off-road vehicles like the H3.
Symptoms of a Failing Hummer H3 Engine Computer:
- โ Check Engine Light is on with communication-related fault codes (U-codes).
- โ Engine cranks but refuses to start.
- โ Severe hesitation or stumbling during acceleration.
- โ Unexplained drop in fuel economy.
- โ Transmission shifting issues or harsh shifts.
- โ Intermittent stalling for no apparent reason.
Simple, Plug-and-Play Installation Guide
You don’t need to be a master technician to get your Hummer running right again. The ECM is located in a very accessible spot. Follow these simple steps:
- Safety First: Always disconnect the negative terminal from your vehicle’s battery and wait a few minutes before starting work.
- Locate the ECM: On your Hummer H3, the Engine Control Module is mounted to the firewall on the passenger side of the engine compartment.
- Disconnect the Connectors: Carefully unclip and disconnect the electrical harness connectors from the old module. The levers can be stiff, so apply steady pressure.
- Remove the Old Module: Unbolt the old ECM from its mounting bracket on the firewall.
- Install the New Module: Mount your new, pre-programmed ECM in place and secure the bolts.
- Reconnect Everything: Firmly plug the harness connectors into the new module until they click into place. Reconnect your battery terminal.
- Final Step: Start your vehicle. It may take a moment to idle smoothly as it completes its internal checks. Your H3 is ready to go!
Guaranteed Compatibility & Interchange Information
This module is a direct replacement for part number 12636659 and is also interchangeable with the following GM service numbers: 12639300, 1263605, 12628993, 12628911, 12625453, 12622175, 12630464, and 12678512. While this listing is focused on the Hummer H3, this versatile ECM also fits a wide range of other GM vehicles, including select models of the Cadillac CTS, STS, XLR, Corvette, Chevy Colorado, GMC Canyon, and more. Providing your VIN ensures we deliver a perfectly matched and updated module for your specific application.