Restore Your Truck’s Brain and Get Back to Work
Is your Sierra 3500 suddenly stalling, shifting erratically, or showing a persistent Check Engine Light? As a technician with over two decades of experience under the hood, I’ve seen these symptoms countless times, and they often point directly to a failing Engine Control Module (ECM). The ECM is the central computer of your truck, managing everything from fuel mixture and ignition timing to transmission shifts. When it starts to fail, it can cause a cascade of frustrating and unpredictable problems that can take your reliable workhorse off the road.
This isn’t just a replacement part; it’s a complete, ready-to-install solution. We take the hassle and high cost out of the equation by pre-programming this genuine GM ECM with the latest factory software updates, tailored specifically to your truck’s Vehicle Identification Number (VIN). This means you can bypass the expensive trip to the dealership for programming. Simply provide us with your VIN at checkout, and we’ll handle the complex software side, shipping you a module that’s ready for a straightforward installation.
Case Study: A Tricky Diagnosis
I remember a 2014 Sierra 2500 with the 6.0L that came into my shop with a bizarre issue: it would run perfectly for 15 minutes, then suddenly lose power and throw a dozen communication error codes (U-codes). The owner had already replaced the throttle body and a wheel speed sensor based on other shops’ advice. After checking the network wiring, my gut told me it was the ECM. Heat soak was causing an internal processor fault, but only after it reached operating temperature. We installed a VIN-programmed module just like this one, and the truck ran perfectly. It’s a classic example of how a faulty ECM can send you chasing ghosts, and why a reliable, correctly programmed module is the only true fix.
Is Your Truck Showing These Symptoms?
A failing ECM can manifest in many ways. If you’re experiencing any of the following, it’s a strong indicator that your engine’s computer needs attention:
- ✔ Unexplained Check Engine Light (CEL)
- ✔ Engine stalling, stumbling, or misfiring
- ✔ Drastic decrease in fuel economy
- ✔ Harsh or incorrect automatic transmission shifting
- ✔ No-start or hard-start conditions
- ✔ Communication error codes, such as U0100 (Lost Communication with ECM/PCM)
- ✔ Internal module failure codes, like P0601 or P0606
- ✔ Failure to pass an emissions inspection
A Straightforward Guide to Installation
Replacing the ECM on your Sierra is a manageable job for a DIYer with basic tools. Our pre-programmed module makes it even simpler. Follow these general steps to get your truck running smoothly again.
- Safety First: Always disconnect the negative terminal from your truck’s battery and wait at least 15 minutes for the system capacitors to discharge.
- Locate the ECM: On most 2012-2016 Sierra HD trucks, the ECM is located in the engine bay, on the driver’s side 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. Never force them. Inspect the connectors for any corrosion or damage.
- Remove the Old Module: Unbolt the mounting hardware that secures the old ECM to its bracket. Note the orientation before removing it.
- Install the New ECM: Mount your new, pre-programmed ECM in the same position and secure it with the original hardware.
- Reconnect and Secure: Plug the electrical harnesses back into the new module until they click firmly into place. Reconnect the negative battery terminal.
- Perform Security Relearn: You will need to perform a simple security relearn procedure (often called a ‘key-on’ or ‘anti-theft’ relearn) so the new ECM recognizes your vehicle’s keys. This procedure typically takes about 30 minutes and does not require special tools. Instructions are readily available online for your specific model.
Verified Vehicle Compatibility
This ECM, part number 12668866, is a direct replacement for a wide range of General Motors vehicles. It is compatible with multiple part numbers, including 12668994, 12643636, 12663405, 12670335, 22819494, and 12692200. Please verify your vehicle from the list below:
ENCORE 13-14 (1.4L)
ENCORE 15 (1.4L), ID 12643636 or 12668866
ENCORE 16 (1.4L), VIN B (8th digit, opt LUV)
Cadillac:
ELR 14-16 (gasoline)
Chevrolet:
CRUZE 12-14 (1.4L / gasoline)
CRUZE 15 (gasoline), ID 12643636 or 12668866
CRUZE 16 VIN P (4th digit, Limited)
EXPRESS 2500/3500 VAN 16 (4.8L or 6.0L)
SILVERADO 2500/3500 PICKUP 12-16 (6.0L)
SONIC 12 (1.4L)
SONIC 13-14 ID 12643636
SONIC 15 ID 12643636 or 12668866
SONIC 16
SPARK 14-15 (gasoline model)
SUBURBAN 3500 16
TRAX 13-16
VOLT 11-15 (gasoline)
GMC:
SAVANA 2500/3500 VAN 16 (4.8L or 6.0L)
SIERRA 2500/3500 PICKUP 12-16 (6.0L)
SIERRA DENALI 2500 12-15 (6.0L)
SIERRA DENALI 3500 12-16 (6.0L)
Frequently Asked Questions
Frequently Asked Questions
Do I need to do anything after installing this ECM?
Yes. While the main engine programming is done for you, you must perform a standard GM Security Relearn Procedure. This syncs the new ECM to your vehicle’s anti-theft system and can be done without special tools in about 30 minutes.
How do I provide my VIN?
Simply enter your 17-digit VIN in the designated box during the checkout process, or send it to us in a message after your purchase. We cannot program and ship the module without it.
Is this a guaranteed fix for my truck’s problems?
This module is a direct solution for a failed ECM. If your vehicle has been properly diagnosed with a faulty ECM, this part will resolve the related issues. It will not fix other mechanical or electrical problems (e.g., a bad fuel pump or faulty sensor).
Will this fix my emissions test failure?
In many cases, yes. A faulty ECM is a common cause of emissions failures due to incorrect air/fuel mixture or sensor readings. A new, properly programmed ECM restores these functions to factory specifications.
What happens if I don’t perform the security relearn?
If the security relearn is not performed, your truck will not start. The anti-theft system will prevent the engine from firing as a security measure. This is a normal and required step for this repair.