Get Your Sierra Back on the Job, Fast.
When your GMC Sierra 3500 is down, the work stops. A faulty Engine Control Module (ECM) can bring your entire operation to a halt, causing frustrating issues like a no-start condition, poor performance, or a persistent Check Engine Light. This isn’t just an inconvenience; it’s a direct hit to your productivity. We provide the definitive solution: a replacement Engine Control Module, part number 12668991, delivered to your door fully programmed and ready for installation. We take your vehicle’s unique VIN and flash the module with the latest, most stable software updates directly from GM, ensuring your truck performs exactly as the manufacturer intended.
Common Symptoms & Your Solution
If your truck is experiencing any of the following, a failing ECM is the likely culprit. This module is the direct-fit, pre-programmed solution to restore your vehicle’s critical systems.
- Persistent Check Engine Light (CEL)
- Diagnostic Trouble Codes (DTCs) related to the processor, such as P0606
- Engine stalling, misfiring, or running rough
- No-start or intermittent starting issues
- Poor fuel economy and reduced power
- Communication errors with diagnostic scan tools
- Erratic transmission shifting behavior
Features & Benefits
- ✔ Plug & Play Installation: Arrives pre-programmed to your truck’s specific VIN. No expensive trip to the dealership for programming is required.
- ✔ Updated GM Software: We flash each unit with the newest factory software, ensuring optimal engine performance, fuel efficiency, and emissions control.
- ✔ Restored Dependability: Resolves common ECM-related fault codes and performance issues, getting your reliable workhorse back on the road.
- ✔ Guaranteed Compatibility: This is a direct replacement for multiple part numbers, including 12668866, 12668994, 12643636, and more. See our full fitment list.
- ✔ Peace of Mind Protection: This unit is backed by our one-year replacement warranty.
Expert Insight: More Than Just a Computer
On a heavy-duty truck like the Sierra 3500, the ECM is the central command for more than just the engine. It’s intricately linked to the transmission control module, the anti-lock brake system, and even the body control module. When we program this unit with the latest GM software, we’re not just loading data; we’re ensuring all these critical systems communicate flawlessly. This proper calibration is key to correct transmission shift points under load, accurate fuel delivery for towing, and the overall longevity of your powertrain. Skipping this step or using a generic, non-programmed module can lead to a cascade of new problems. Our VIN-specific programming service ensures every component works in harmony, just as it did from the factory.
Frequently Asked Questions
Do I need to do any additional programming after installation?
No. This GMC Sierra 3500 ECM 12668991 arrives fully programmed to your vehicle’s VIN. In most cases, it is a direct installation. However, some vehicles may require a security relearn procedure (often called a CASE relearn or anti-theft relearn), which can typically be done without special tools. Instructions are widely available online for this simple process.
How does the programming process work?
After you place your order, you will need to provide us with your vehicle’s 17-digit VIN. Our technicians use this VIN to access the official GM database and download the correct, most up-to-date software calibration for your specific truck. We then flash this software onto the module before shipping it to you.
Is this ECM compatible with other vehicles besides the Sierra?
Yes. While this listing is focused on the GMC Sierra 3500 ECM 12668991, this part number is a compatible replacement for a wide range of GM vehicles, including the Silverado, Express/Savana vans, Cruze, Sonic, and more. Please check the detailed fitment list on this page to confirm compatibility with your specific make, model, and year.
What if my original part number isn’t an exact match?
This module replaces several original equipment part numbers, including 12668866, 12668994, and 12643636. As long as your vehicle is on our fitment list and your original part number is listed as an interchangeable part, this module will work correctly once programmed to your VIN.
Where can I find my vehicle’s VIN?
Your 17-digit Vehicle Identification Number (VIN) can be found on your vehicle’s registration, your insurance card, or on a metal plate located on the driver’s side of the dashboard, visible through the windshield.