Restore Peak Performance to Your Sierra HD
Is your 2012-2016 Sierra Denali 2500 suffering from baffling electrical issues, poor engine performance, or a persistent check engine light? A failing Engine Control Module (ECM) is often the culprit behind these frustrating problems. As the brain of your truck’s powertrain, a faulty ECM can lead to everything from rough idling and stalling to incorrect shifting and even a no-start condition. Don’t let a bad computer sideline your powerful workhorse. This replacement ECM, part number 12668991, is the reliable, straightforward solution you need to get your truck running like new again.
With over 20 years of hands-on diagnostic experience, I’ve seen firsthand how a failing ECM can mimic a dozen other problems, costing owners time and money on unnecessary repairs. That’s why we offer a solution designed for confidence and ease. We take the guesswork and hassle out of the replacement process by pre-programming this module specifically for your vehicle. Simply provide us with your VIN during checkout, and our technicians will flash the unit with the latest, most stable GM software updates. This ensures perfect communication between the ECM and all other systems in your truck, restoring factory performance and efficiency.
From the Diagnostic Bay: The Case of the Intermittent No-Start
A customer brought in his 2014 Sierra 2500 with the 6.0L V8. The complaint was maddening: some mornings it would start perfectly, other times it would just crank and crank. He’d already replaced the battery and checked the fuel pump. We scanned it and found a U0100 (Lost Communication with ECM) code stored, but no active faults. After verifying all power and ground connections to the module were solid—a critical first step I always perform—we suspected the ECM itself was failing internally, especially when exposed to heat soak after a long drive. We installed a pre-programmed ECM, and the problem vanished instantly. It’s a classic scenario where the module’s internal circuits break down intermittently, causing symptoms that can lead you on a wild goose chase.
Is Your Sierra HD Showing These Symptoms?
A failing engine computer can manifest in numerous ways. If you’re experiencing any of the following, a faulty ECM could be the root cause:
- ✔ Check Engine Light is illuminated with communication-related codes (e.g., U0100) or internal processor fault codes (P0601, P0606).
- ✔ Engine cranks but refuses to start.
- ✔ Unexplained stalling or rough idling.
- ✔ Noticeable decrease in fuel economy.
- ✔ Harsh or erratic automatic transmission shifting.
- ✔ Apparent loss of engine power and throttle response.
- ✔ Other warning lights on the dash appear randomly.
A Straightforward Guide to Your 2012-2016 Sierra Denali 2500 ECM Installation
Replacing the ECM on these trucks is a job most DIYers can handle with basic tools. Our pre-programming service eliminates the need for expensive dealer tools.
- Safety First: Disconnect the negative terminal from your vehicle’s battery and secure it away from the post to prevent accidental contact.
- Locate the ECM: On the 2012-2016 Sierra/Silverado HD, the ECM is typically located in the engine bay on the driver’s side, near the firewall or inner fender.
- Disconnect the Connectors: Carefully release the locking tabs on the electrical connectors and pull them straight out from the module. Avoid pulling on the wires themselves.
- Remove the Old Module: Unbolt the old ECM from its mounting bracket. There are usually a few 10mm bolts holding it in place.
- Install the New Module: Mount your new, pre-programmed ECM onto the bracket and secure the bolts.
- Reconnect Everything: Firmly plug the electrical connectors back into the new ECM until they click into place. Reconnect the negative battery terminal.
- Final Steps: In some cases, a security relearn or crank position sensor relearn may be required, which can often be done without a scan tool. Turn the key to the ‘ON’ position for 10-15 minutes, then off, and then start the vehicle.
Verified Vehicle Compatibility
This module is a direct replacement for part number 12668991 and is also compatible with part numbers 12668866, 12668994, 12643636, 12663405, 12670335, 22819494, and 12692200. It fits a wide range of GM vehicles, including:
- Chevrolet Silverado 2500/3500 (2012-2016) with 6.0L engine
- GMC Sierra 2500/3500 & Denali (2012-2016) with 6.0L engine
- Chevrolet Express / GMC Savana 2500/3500 (2016) with 4.8L or 6.0L engine
- Chevrolet Suburban 3500 (2016)
- Chevrolet Cruze (2012-2016) – various engines/options
- Chevrolet Sonic (2012-2016) – various engines/options
- Chevrolet Trax (2013-2016)
- Chevrolet Spark (2014-2015) – gasoline models
- Chevrolet Volt (2011-2015)
- Buick Encore (2013-2016) – 1.4L engine
- Cadillac ELR (2014-2016)
Frequently Asked Questions
Why do you need my VIN?
Your Vehicle Identification Number (VIN) is essential. It allows us to program the ECM with the exact software and calibrations specific to your truck’s engine, transmission, and factory options. This ensures seamless integration and proper function without a trip to the dealer.
Is this a simple plug-and-play installation?
Yes, for the vast majority of vehicles. Because we pre-program the module, you can typically install it and start the vehicle. In some rare cases, a simple, key-on security relearn procedure may be necessary, which does not require special tools.
Will this fix my check engine light?
If the check engine light is caused by an internal failure of the ECM (like codes P0601-P0606) or communication errors (U-codes), then yes, this part is the correct fix. However, it’s always best to properly diagnose the codes to ensure another sensor or component isn’t the root cause.
What if I have a different part number on my old ECM?
This ECM replaces several common GM part numbers, including 12668866, 12668994, 12643636, and more. Check the full compatibility list in our description. As long as your vehicle and engine are listed, this module will work perfectly once programmed to your VIN.