Restore Peak Performance to Your GM Truck
As a technician with over two decades of experience under the hood, I understand the frustration that comes with a failing Engine Control Module (ECM). Your 2012-2016 Sierra Denali 3500 is a workhorse, but when its electronic brain starts to glitch, it can lead to a host of problems—from poor fuel economy and rough idling to a dreaded no-start condition that leaves you stranded. This isn’t just an inconvenience; it’s a blow to your truck’s reliability and your peace of mind.
This replacement Engine Control Module, part number 12668991, is the definitive solution. It’s not just a part; it’s a fresh start for your vehicle’s engine management system. We take the guesswork and hassle out of the replacement process. Before this module ever ships, our specialists will program it with the latest official GM software, specifically matched to your truck’s Vehicle Identification Number (VIN). This ensures seamless integration and optimal performance right out of the box, restoring the precise fuel delivery, ignition timing, and emissions control your engine was designed for.
A Technician’s Notebook
I remember a 2014 Sierra 2500 with the 6.0L that came into the shop with a truly baffling issue. The owner complained of random stalling at stoplights and an intermittent check engine light. We scanned it and found a P0606 (ECM/PCM Processor Fault) code, but it wasn’t always present. After checking all the wiring harnesses for chafing and verifying power and ground at the ECM connector, everything seemed fine. The truck would run perfectly for days, then act up again. This is a classic sign of internal ECM failure, often due to thermal stress causing microscopic breaks in the circuit board. We installed a VIN-programmed module just like this one, performed the security relearn, and the problem was solved for good. It’s a reminder that sometimes the most elusive electrical gremlins live inside the box itself.
Is Your Truck Showing These Symptoms?
A faulty ECM can manifest in numerous ways. If you’re experiencing any of the following, it’s a strong indicator that your engine’s computer needs attention:
- ✔ Check Engine Light is on with codes like P0601, P0606, or U0100
- ✔ The engine cranks but refuses to start
- ✔ Unexplained drop in fuel efficiency
- ✔ Rough or erratic idling
- ✔ Hesitation or stumbling during acceleration
- ✔ Transmission shifting issues or harsh shifts
- ✔ Communication errors with other vehicle modules
Your Solution: A Reliable 2012-2016 Sierra 3500 ECM
Choosing this pre-programmed module means you’re getting a part that is ready for installation, saving you a costly trip to the dealership for programming. It’s the most efficient way to get your heavy-duty truck back to its factory-spec operational state. By providing us with your VIN at checkout, you ensure that the software loaded onto this computer is perfectly tailored to your vehicle’s specific options and systems.
A Straightforward Guide to Installation
Replacing the ECM is a manageable job for a DIY enthusiast or a quick task for a professional. Follow these steps for a successful installation:
- Safety First: Always disconnect the negative terminal from your truck’s battery and secure it away from the post.
- Locate the ECM: On most 2012-2016 Sierra and Silverado HD trucks, the ECM is located in the engine bay on the driver’s side, near the firewall or inner fender.
- Disconnect 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. Keep the hardware, as you may need it for the new installation.
- Install the New ECM: Mount the new module securely onto the bracket and re-tighten the bolts.
- Reconnect Everything: Plug the electrical connectors firmly back into the new ECM until they click into place. Reconnect the negative battery terminal.
- Perform Security Relearn: You will need to perform a security relearn procedure (often called a Passlock or Passkey relearn) to sync the new ECM with your truck’s anti-theft system. This typically involves turning the key to the ‘ON’ position for 10-15 minutes, then off, and repeating the cycle two more times. Your vehicle’s service manual will have the precise steps.
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:
EXPRESS/SAVANA 2500 & 3500 VANS (2016) with 4.8L or 6.0L engines
SILVERADO/SIERRA 2500 & 3500 PICKUPS (2012-2016) with 6.0L engines
SIERRA DENALI 2500 (2012-2015) & 3500 (2012-2016) with 6.0L engines
SUBURBAN 3500 (2016)
Please verify your vehicle’s part number or contact us with your VIN to confirm an exact match.
Frequently Asked Questions
Do I need to do anything after I buy this?
Yes. After your purchase, you must provide us with your vehicle’s 17-digit VIN. We cannot program and ship the module without it. This ensures the software is a perfect match for your truck.
Is this part difficult to install?
The physical installation is straightforward for anyone with basic mechanical skills. However, you MUST perform a security relearn procedure after installation for the vehicle to start. This procedure is simple and does not require special tools.
What is the benefit of a pre-programmed module?
It saves you time and money. A non-programmed module would require a trip to a dealership or a well-equipped shop for expensive programming. Our service handles that for you, so the part is ready to install when it arrives.
Will this fix my Check Engine Light?
If the Check Engine Light is on due to an internal ECM failure (like codes P0601 or P0606), this part will resolve the issue. It’s crucial to properly diagnose the problem first, as the light could be on for other reasons.
Does this ECM fit other vehicles besides the Sierra?
Yes, this is a widely used ECM across the GM lineup. It fits many trucks, vans, and even some cars like the Cruze and Sonic. Please check the detailed compatibility list to be certain.