2004 Sierra 3500 ECM 12586243 | Programmed to Your VIN | Engine Control Module

Restore Peak Performance to Your GM Truck’s Engine

Is your 2004 GMC Sierra 3500 Pickup struggling with erratic behavior like stalling, poor fuel mileage, or a persistent Check Engine Light? These are classic signs that the heart of your engine management system—the Engine Control Module (ECM)—is failing. As the central computer, the ECM controls everything from fuel injection and ignition timing to transmission shifting. When it falters, it can cause a host of frustrating and hard-to-diagnose problems. This replacement 2004 Sierra 3500 ECM, part number 12586243, is the reliable, plug-and-play solution you need to get your workhorse running smoothly again.

We take the guesswork and high cost out of the repair. Unlike a generic module from a parts store, this unit arrives at your door pre-programmed with the latest official GM software updates, specifically matched to your truck’s Vehicle Identification Number (VIN). This means you can skip the expensive trip to the dealership for programming. It’s a direct-fit replacement designed to restore factory performance and reliability.

Is Your GM Truck Showing These Signs of ECM Failure?

A failing engine computer can manifest in numerous ways. If you’re experiencing any of the following, a faulty ECM could be the culprit:

• ✔ Check Engine Light is on with codes like P0601 (Internal Memory Error) or P0606 (PCM Processor Fault)
• ✔ Engine cranks but refuses to start
• ✔ Unexplained drops in fuel economy
• ✔ Rough or unstable idle
• ✔ Vehicle stalling for no apparent reason
• ✔ Harsh or erratic automatic transmission shifting
• ✔ Loss of power and sluggish acceleration
• ✔ Scan tool cannot communicate with the ECM

Your Straightforward Installation Guide

Installing your new 2004 Sierra 3500 ECM is a manageable job for a confident DIYer. For the Sierra 3500, the module is typically located on the driver’s side, in the engine bay, under or near the battery tray. Always consult a repair manual for your specific vehicle’s location and torque specs.

1. Safety First: Disconnect the negative terminal from your vehicle’s battery and secure it away from the post to prevent accidental reconnection.
2. Locate and Access the ECM: On the 2004 Sierra 3500, you will likely need to remove the battery to access the ECM mounted below it.
3. Disconnect Wiring Harnesses: Carefully disengage 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.
4. Remove the Old Module: Unbolt the old ECM from its mounting bracket. Keep the hardware as you will need it for the new module.
5. Install the New ECM: Mount the new module securely onto the bracket and tighten the bolts.
6. Reconnect Everything: Plug the wiring harnesses firmly back into the new ECM until they click into place. Reinstall and reconnect the battery.
7. Perform Security Relearn: After installation, you must perform a security relearn procedure (often called a Passlock or anti-theft relearn). This typically involves turning the key to the ‘ON’ position for 10-15 minutes, then ‘OFF’, and repeating two more times. This allows the new ECM to sync with your vehicle’s anti-theft system.

Verified Compatibility for Your GM Vehicle

This module, service number 12586243 (interchangeable with 89017739), is a guaranteed fit for a wide range of 2004 and 2005 GM trucks, vans, and performance cars. Please verify your vehicle is on this list and provide your VIN upon purchase to ensure perfect programming.