Restore Your Truck’s Core Performance and Reliability
As a technician with over two decades of experience under the hood, I’ve seen firsthand how a failing Engine Control Module (ECM) can turn a reliable workhorse like a Sierra 3500 into a source of constant frustration. The ECM is the brain of your engine, managing everything from fuel injection and ignition timing to transmission shifts and emissions controls. When it starts to fail, you’re not just dealing with a check engine light; you’re facing unpredictable performance, poor fuel economy, and even a no-start condition that can leave you stranded. This isn’t just an inconvenience—it’s a critical failure that compromises your truck’s ability to do its job.
This replacement Engine Control Module, part number 12668991, is the definitive solution to these complex issues. What sets this module apart is our professional programming service. Before we ship it, we flash the module with the latest official GM software, specifically matched to your truck’s Vehicle Identification Number (VIN). This means you receive a component that is ready for installation right out of the box, eliminating the need for expensive dealership programming or specialized scan tools. It’s a direct-fit, plug-and-play solution designed to get your truck running right again, quickly and affordably.
Case Study: The Ghost in the Machine
I remember a 2014 Silverado 2500 (which uses a similar system to the Sierra) that came into the shop with a list of bizarre, intermittent problems. The owner complained of random stalling at idle, harsh shifting, and a flickering check engine light with no consistent codes. We checked everything—fuel pressure, sensors, wiring harnesses—and found nothing conclusive. It was a classic ‘ghost in the machine’ scenario. On a hunch, we swapped in a known-good, programmed ECM. The change was immediate. Every single issue vanished. The original ECM had internal circuit board failures that were causing unpredictable data corruption. This is a perfect example of how a single component, the 2012-2016 Sierra 3500 Engine Control Module, can be the root cause of multiple, seemingly unrelated symptoms.
Is Your Truck Showing These Symptoms?
A failing ECM can manifest in numerous ways. If you’re experiencing any of the following, it’s a strong indicator that your engine’s computer may need replacement:
- ✔ Persistent Check Engine Light (CEL) that won’t clear
- ✔ Diagnostic Trouble Codes (DTCs) related to internal processor failure, such as P0601, P0606, or U0100
- ✔ Engine cranks but refuses to start
- ✔ Noticeable drop in fuel economy
- ✔ Rough or unstable idling
- ✔ Engine stalling or misfiring unexpectedly
- ✔ Harsh or erratic automatic transmission shifting
- ✔ Communication errors with diagnostic scan tools
A Straightforward Guide to Installation
Replacing the ECM on your Sierra or Silverado HD is a manageable job for a confident DIYer. Our pre-programming service handles the most difficult part. Here’s a basic overview of the process:
- Safety First: Always disconnect the negative terminal from your vehicle’s battery and wait a few minutes for the system to fully discharge.
- Locate the ECM: On most 2012-2016 GM HD trucks, the ECM is 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 large wiring harness connectors and pull them straight out from the module. Avoid pulling on the wires themselves.
- Remove the Module: Unbolt the old ECM from its mounting bracket. It’s typically held in place by a few bolts or nuts.
- Install the New ECM: Mount your new, pre-programmed module in place and tighten the fasteners.
- Reconnect Everything: Firmly plug the wiring harness connectors back into the new ECM until they click and lock. Reconnect the negative battery terminal.
- Final Steps: In some cases, a security relearn procedure may be required, which can typically be done without special tools by cycling the key. Your vehicle’s service manual will have the specific steps. Start the engine and verify that the check engine light is off and the truck runs smoothly.
Why Choose Our Programmed 2012-2016 Sierra 3500 Engine Control Module?
Choosing this module means you’re not just buying a part; you’re buying a complete, ready-to-install solution. By providing us with your VIN, you ensure that the module you receive is loaded with the correct software for your truck’s specific configuration, including engine, transmission, and emissions equipment. This restores factory performance and communication between all vehicle systems. Don’t let a faulty computer keep your truck off the road—get the reliable, pre-programmed fix you need.
Verified Vehicle Compatibility
This module is a direct replacement for part number 12668991 and is compatible with several other part numbers, including 12668866, 12668994, 12643636, and more. It fits a wide array of GM vehicles. Please verify your part number or contact us with your VIN to confirm fitment.
SILVERADO 3500 PICKUP 12-16 Electronic Control Module; (LH front engine compartment), 6.0L
SIERRA 2500 PICKUP 12-16 Electronic Control Module; (LH front engine compartment), 6.0L
SILVERADO 2500 PICKUP 12-16 Electronic Control Module; (LH front engine compartment), 6.0L
SIERRA DENALI 2500 12-15 Electronic Control Module; (LH front engine compartment), 6.0L
SIERRA DENALI 3500 12-16 Electronic Control Module; (LH front engine compartment), 6.0L
EXPRESS 2500/3500 VAN 16 Electronic Control Module; 4.8L or 6.0L
SAVANA 2500/3500 VAN 16 Electronic Control Module; 4.8L or 6.0L
SUBURBAN 3500 16 Electronic Control Module; (LH front engine compartment)
CRUZE 12-15 (Gasoline, various IDs)
CRUZE 16 (VIN P, Limited)
SONIC 12-16 (1.4L or specific IDs)
TRAX 13-16
ENCORE 13-16 (1.4L)
VOLT 11-15
ELR 14-16
SPARK 14-15 (Gasoline model)
Frequently Asked Questions
What do you mean by ‘programmed to my VIN’?
Every vehicle has a unique Vehicle Identification Number (VIN) that contains information about its specific options, engine, and emissions systems. We use your VIN to load the exact GM factory software for your truck onto the ECM before shipping. This ensures perfect compatibility and function without needing a trip to the dealer.
Do I need to do anything after installation?
In most cases, this is a plug-and-play solution. However, some GM vehicles require a security or anti-theft relearn procedure after the ECM is replaced. This is a simple process that usually involves cycling the ignition key and can be done in your driveway. We can provide instructions if needed.
Will this fix my check engine light?
If the check engine light is caused by an internal failure of the old ECM (like codes P0601 or P0606), then yes, this new module will resolve the issue. If the light is on for another reason, such as a bad sensor, that component will still need to be addressed separately.
Is this a new or used part?
This is a high-quality, inspected, and tested used OEM component. Each unit is verified to be fully functional before being professionally programmed with the latest software for your vehicle, offering a reliable and cost-effective alternative to a brand-new dealership part.
How do I provide my VIN?
After you complete your purchase, simply send us a message with your 17-digit VIN. We cannot program and ship your module without it, so please provide it promptly to avoid delays.