Restore Peak Performance to Your GM Truck or Car
Is your vehicle suffering from frustrating issues like intermittent stalling, a persistent check engine light, or a sudden drop in fuel economy? These aren’t just annoyances; they’re often symptoms of a failing Engine Control Module (ECM), the computer that serves as the brain of your engine. When the ECM falters, it can lead to a cascade of performance problems, leaving you stranded or facing costly, incorrect repairs. As a technician with over two decades of experience, I’ve seen firsthand how a faulty ECM can mimic other component failures, leading to wasted time and money on parts you don’t need.
This replacement Engine Control Module, part number 12668866, is the definitive solution. We take the guesswork and hassle out of the replacement process. Before we ship it, we will professionally program the module with the latest official GM software updates, tailored specifically to your vehicle’s VIN. This means no expensive trips to the dealership for programming. It arrives at your door ready for a straightforward installation, designed to restore the precise engine management your vehicle had when it left the factory. Get your truck or car running reliably again with this plug-and-play solution.
A Technician’s Notebook: The Ghost in the Machine
A customer brought in a 2014 Sierra 2500 with the 6.0L V8, complaining of a random, violent stumble under load—almost like the ignition cut out for a split second. No consistent codes were stored, just a history of random misfires. We checked plugs, coils, and even fuel pressure, all of which were perfect. The symptoms were so intermittent, they were impossible to replicate consistently in the bay. After hooking up a high-speed data logger, I finally caught it: a momentary drop in the 5-volt reference signal from the ECM. The module itself was failing internally under specific thermal conditions. We installed a VIN-programmed 2012-2016 Sierra Denali 3500 ECM, and the problem was solved instantly. It’s a classic case where the ECM is the last thing people suspect, but often the root cause of the most elusive issues.
Is Your Vehicle Showing These Symptoms?
- ✔ Check Engine Light (CEL) is on with codes like P0601, P0606, or other internal processor faults.
- ✔ Engine cranks but refuses to start.
- ✔ Unexplained drop in fuel mileage.
- ✔ Noticeable loss of power and poor acceleration.
- ✔ Rough or erratic idling and stalling.
- ✔ Harsh or incorrect automatic transmission shifting.
- ✔ Failure to pass state emissions testing.
A Straightforward Guide to Installation
Replacing the ECM is a manageable job for a confident DIYer. By following these steps, you can get your vehicle back on the road without a trip to the shop. For this specific 2012-2016 Sierra Denali 3500 ECM, the module is typically located in the front, left-hand side of the engine compartment.
- Safety First: Always disconnect the negative terminal from your vehicle’s battery and wait at least 10 minutes to allow the system to fully discharge.
- Locate the ECM: On most Sierra/Silverado models, it’s mounted on the driver’s side of the engine bay, near the firewall or inner fender.
- Disconnect the Harnesses: Carefully release the locking tabs on the electrical connectors and pull them straight out from the module. Do not force them. Inspect the pins for any corrosion or damage.
- Remove the Module: Unbolt the old ECM from its mounting bracket. Keep the hardware, as you may need to reuse it.
- Install the New ECM: Mount your new, pre-programmed ECM in place and secure it with the original hardware.
- Reconnect Everything: Firmly plug the electrical harnesses back into the new module until they click, ensuring a secure connection. Reconnect the negative battery terminal.
- Perform Security Relearn: Your vehicle may require a simple Key Relearn Procedure to sync with the new ECM. This typically involves turning the key to the ‘ON’ position for 10-15 minutes, then ‘OFF’, and repeating two more times before starting the engine. Consult your owner’s manual for the exact procedure for your model.
Verified Vehicle Compatibility
This module is a direct replacement for part numbers 12668866, 12668994, 12643636, 12663405, 12670335, 22819494, and 12692200. It is guaranteed to fit the following GM vehicles. Please ensure your model and options match the list below.
SONIC 12-16 (multiple engine/ID options)
ELR 14-16
EXPRESS 2500/3500 VAN 16 (4.8L, 6.0L)
SAVANA 2500/3500 VAN 16 (4.8L, 6.0L)
SILVERADO 2500/3500 PICKUP 12-16 (6.0L)
SIERRA 2500/3500 PICKUP 12-16 (6.0L)
SIERRA DENALI 2500 12-15 (6.0L)
SIERRA DENALI 3500 12-16 (6.0L)
SUBURBAN 3500 16
VOLT 11-15
TRAX 13-16
ENCORE 13-16 (1.4L)
SPARK 14-15 (gasoline model)
Frequently Asked Questions
Do I need to do any programming myself?
No. We handle all the programming for you before shipment. Simply provide your vehicle’s 17-digit VIN during checkout, and we will flash the module with the correct, updated GM software for your specific vehicle. It arrives ready to install.
Is this a simple plug-and-play installation?
Yes, for the most part. Once you install the module, you will need to perform a quick security relearn procedure (also known as a key relearn). This procedure is simple, requires no special tools, and instructions are included with your purchase. It syncs the new ECM to your vehicle’s anti-theft system.
How do I find my vehicle’s VIN?
Your VIN can be found on your vehicle’s registration, insurance card, or on the driver’s side of the dashboard, visible through the windshield. It is critical that you provide the full, correct 17-digit VIN for accurate programming.
Will this fix my check engine light?
If the check engine light is caused by an internal failure of the ECM (common codes include P0601-P0606), then this part will resolve the issue. However, if the light is on due to a faulty sensor or other component, you will still need to diagnose and repair that separate issue.
What if I have the wrong part number?
This module replaces a wide range of part numbers, including 12668866, 12668994, 12643636, and more as listed above. As long as your vehicle is on the compatibility list, this module will function correctly once programmed to your VIN.