Is Your 6.6L Duramax Running Rough? It Could Be The ECM.
The Engine Control Module (ECM) is the electronic brain of your 2014-2015 GMC Savana, Sierra, or Chevrolet Silverado/Express. When it begins to fail, it can cause a cascade of confusing and frustrating problems that can bring your powerful 6.6L Duramax diesel engine to a halt. From a persistent check engine light to a complete no-start condition, a faulty ECM can mimic a wide range of other mechanical issues. This direct replacement ECM, part number 12667377 (also interchangeable with 12658036), is the definitive solution to restore your truck or van’s performance and reliability.
From the Diagnostic Bay
We had a 2015 Silverado 2500 towed in that was driving the owner crazy. It would randomly stall at idle, had intermittent power loss on the highway, and the transmission was shifting erratically. The owner had already replaced the fuel filter and a couple of sensors with no luck. After hooking up our diagnostic tools, we noticed intermittent communication drops with the engine module. We couldn’t find any wiring issues, so we focused on the ECM itself. After installing a freshly programmed module, all the strange symptoms vanished. The truck ran smoother than it had in years. It’s a classic case of how a failing ECM can send you chasing ghosts all over the vehicle.
Common Symptoms of a Failing 2014-2015 Duramax ECM
- ✔ Persistent Check Engine Light (CEL) with communication-related fault codes (U-codes).
- ✔ Engine stalling, stumbling, or misfiring for no apparent reason.
- ✔ A complete no-start condition where the engine cranks but will not fire up.
- ✔ Noticeable decrease in fuel economy and engine performance.
- ✔ Problems with automatic transmission shifting, such as harsh or delayed shifts.
- ✔ Inability for diagnostic scan tools to communicate with the engine module.
- ✔ Issues with other electronic systems that rely on data from the ECM.
The Right Part, Programmed For Your Vehicle
Don’t settle for a generic, unprogrammed module that will cause more headaches than it solves. We take the guesswork out of the repair by programming this ECM specifically to your vehicle’s 17-digit Vehicle Identification Number (VIN) before it ships. This process loads the latest GM-certified calibrations, ensuring that the module communicates perfectly with your truck’s other systems, from the transmission to the anti-theft system. This VIN-specific programming is essential for proper engine function, emissions compliance, and overall vehicle operation.
Installation and Required Relearn Procedures
While this part is a direct physical replacement, some electronic setup is required after installation. This is standard procedure for any ECM replacement on these vehicles.
- Physical Installation: Disconnect the battery. Carefully unplug the wiring harnesses from the old ECM and unbolt it from its mounting location (typically on the LH side of the engine compartment). Install the new module in its place and reconnect everything.
- Vehicle Theft Deterrent System (VTDS) Relearn: This is a mandatory step. After installation, the vehicle will not start until the new ECM is synchronized with your vehicle’s security system. This procedure must be performed by a qualified technician using a GM-compatible diagnostic tool with access to GM’s TIS2Web service.
- Other Relearns: Depending on your vehicle’s specific configuration and any stored trouble codes, other procedures like a crankshaft position variation relearn or injector flow rate programming may be necessary to achieve optimal performance. It is the end user’s responsibility to ensure these procedures are completed by a professional.
Guaranteed Fitment
This ECM is a direct replacement for part numbers 12667377 and 12658036 on the following vehicles equipped with the 6.6L Duramax diesel engine:
- 2014-2015 Chevrolet Express 2500/3500 Van
- 2014-2015 GMC Savana 2500/3500 Van
- 2015 Chevrolet Silverado 2500/3500 Pickup
- 2015 GMC Sierra 2500/3500 Pickup (including Denali)
Frequently Asked Questions
Do I need to program this ECM?
We handle the main programming for you. We flash the module with the correct GM software for your specific VIN before we ship it. However, you will still need to have a mandatory Vehicle Theft Deterrent System (VTDS) relearn performed after installation for the vehicle to start.
What is a security relearn?
A security relearn, or VTDS relearn, is an electronic handshake procedure that pairs the new ECM to your vehicle’s existing anti-theft components, like the ignition switch and Body Control Module. Without this procedure, the security system will assume the vehicle is being stolen and will disable the engine.
Will this fix my check engine light?
If the check engine light is caused by a faulty ECM, then yes, this part will resolve the issue. It is crucial to have a proper diagnosis performed to confirm the ECM is the point of failure before ordering, as this part cannot correct issues with other sensors or mechanical components.
What information do you need from me?
After placing your order, you must provide us with your vehicle’s complete 17-digit VIN. We cannot program or ship your ECM without it. The VIN is typically found on your driver’s side dashboard (visible through the windshield) or on the driver’s door jamb sticker.
Is this part difficult to install?
The physical installation is straightforward for someone with mechanical experience. However, due to the required electronic relearn procedures that need professional tools, we strongly recommend installation by a qualified automotive technician.