Restore Peak Performance to Your GM Vehicle
Is your 2004 Avalanche 2500, Sierra, or Express van running poorly? Experiencing frustrating issues like a persistent check engine light, erratic shifting, or a no-start condition? The Powertrain Control Module (PCM), the electronic brain of your engine and transmission, is often the source of these complex problems. Over time, heat, vibration, and age can cause these critical components to fail. This replacement PCM, part number 12586243, is the reliable, straightforward solution to get your vehicle back on the road and running like it should.
We take the guesswork and high cost out of the repair. Unlike a generic module from a parts store, this unit comes professionally programmed to your vehicle’s specific Vehicle Identification Number (VIN). We install the latest GM-authorized software updates, which can resolve underlying drivability issues you might not even be aware of. This means no expensive trip to the dealership for programming—it arrives ready for installation.
From the Diagnostic Bay: The Intermittent No-Start Nightmare
I remember a 2004 Sierra 2500 with the 8.1L V8 that came into my shop on a tow truck. The owner was fed up. It would start and run perfectly for weeks, then suddenly refuse to start for a day. No codes, no warning. We checked the fuel pump, crank sensor, and ignition system—all tested fine. On a hunch, I tapped the PCM housing under the battery tray while my apprentice cranked the engine, and it fired right up. The problem was an internal fracture on the PCM’s circuit board, a classic symptom of heat and vibration fatigue. We replaced it with a VIN-programmed unit like this one, and the customer never had the issue again. That’s the kind of definitive fix this part provides.
Is Your GM Vehicle Showing These Signs?
A failing PCM can cause a wide range of symptoms. If you’re noticing any of the following, it might be time for a replacement:
- ✔ Persistent Check Engine Light (CEL) with codes like P0601, P0602, P0606 (Internal Controller Failure).
- ✔ Engine stalling, stumbling, or running rough.
- ✔ Unexplained drop in fuel economy.
- ✔ Harsh or erratic automatic transmission shifting.
- ✔ Complete no-start or intermittent starting problems.
- ✔ Communication loss with other vehicle modules (U-codes).
A Straightforward Guide to Installation
Replacing the PCM on most of these GM vehicles is a job a confident DIYer can handle in under an hour. While locations vary slightly, the process is generally the same.
- Safety First: Always disconnect the negative terminal from your vehicle’s battery and secure it away from the post.
- Locate the PCM: On most trucks and SUVs like the 2004 Avalanche 2500, it’s found on the driver’s side, under the battery in a plastic tray. On vans, it’s typically in the rear of the engine compartment on the driver’s side.
- Disconnect Wiring: Carefully unplug the electrical connectors. These GM connectors have locking levers or tabs that need to be released before you can pull them out. Do not force them.
- Remove the Old Module: Unbolt the PCM from its mounting bracket or tray.
- Install the New PCM: Mount the new module securely and reconnect the wiring harnesses. Ensure they click firmly into place.
- Reconnect Battery: Reattach the negative battery terminal.
- Perform Security Relearn: You may need to perform a simple security relearn procedure. Typically, this involves turning the key to the ‘ON’ position for 10-15 minutes, then off, and repeating two more times before starting the engine. This allows the new PCM to sync with your vehicle’s anti-theft system.
Verified Vehicle Compatibility
This module is a direct replacement for part numbers 12586243 and 89017739 and fits a wide array of 2004 GM models. Please verify your vehicle is on this list. Note that some models require matching specific ID codes.
- AVALANCHE 2500: 2004 (LH front under battery)
- ASTRO / SAFARI (GMC): 2004 (LH front by battery)
- BLAZER S10/JIMMY S15: 2004 (RH front engine compartment)
- CORVETTE: 2004 (RH engine compartment, ID 12586243)
- CTS: 2004-2005 (V-Series, RH engine compartment, ID 12586243)
- ENVOY / TRAILBLAZER (XL, EXT, XUV): 2004 (5.3L, various IDs)
- EXPRESS / SAVANA VAN (1500, 2500, 3500): 2004 (LH rear engine compartment)
- GTO: 2004 (Main, LH engine)
- RAINIER: 2004 (5.3L, various IDs)
- S10/S15/SONOMA: 2004 (RH front engine compartment)
- SIERRA / SILVERADO (1500, 2500, 3500): 2004 (Gasoline, various engines)
- SSR: 2004 (various IDs)
- SUBURBAN 2500 / YUKON XL 2500: 2004 (8.1L, LH front under battery)
Frequently Asked Questions
Why do you need my VIN?
Your VIN (Vehicle Identification Number) is essential for us to program the PCM with the correct factory software and calibrations for your specific engine, transmission, and options. This ensures perfect compatibility and performance.
Is this part truly plug-and-play?
Yes, it is. Because we pre-program it to your VIN, you will not need a dealer scan tool for software installation. In some cases, a simple ‘security relearn’ procedure (as outlined in our guide) is needed, which requires no special tools.
What is the difference between a PCM and an ECM?
The terms are often used interchangeably. ECM (Engine Control Module) typically just controls engine functions. A PCM (Powertrain Control Module) is more common and controls both the engine and the automatic transmission, which is the case for this part.
My original part number is 89017739. Will this work?
Yes, this module is a fully compatible replacement for service number 89017739. We ensure the programming matches your vehicle’s requirements exactly.
Do I need to send my old PCM back?
No core charge or return is required for this particular part. You can recycle your old module locally.