Is Your 2004 Blazer or Jimmy Running Rough? Get the Definitive Fix.
As a mechanic with over two decades of experience under the hood, I’ve seen firsthand how a failing Powertrain Control Module (PCM) can turn a reliable truck into a source of constant frustration. If your 2004 Chevy Blazer S10 or GMC Jimmy S15 is experiencing baffling issues like random stalling, poor fuel mileage, a persistent Check Engine Light, or a complete no-start condition, the PCM is often the culprit. This isn’t just a component; it’s the brain of your engine, and when it falters, everything else does too.
This isn’t a generic, one-size-fits-all part. This is a direct-replacement Electronic Control Module (ECM), part number 12586243, that arrives at your door pre-programmed with the latest official GM software updates. We use your vehicle’s VIN to ensure the programming is a perfect match for your specific configuration. This critical step means you can skip the expensive trip to the dealership for programming, saving you both time and hundreds of dollars. You’re getting a reliable solution that restores your vehicle’s performance and efficiency right out of the box.
A Technician’s Notebook: The Misleading Ground Wire
I remember a 2004 GMC Sonoma that came into the shop with all the classic signs of a bad PCM—erratic gauges, stalling, and a handful of communication codes. The owner had already bought a module from another supplier and was frustrated it didn’t fix the issue. Before condemning his new part, I did my due diligence. I went straight to the main engine-to-chassis ground strap. Sure enough, it was corroded and barely making contact. After cleaning the connection points and tightening the strap, every single symptom disappeared. A failing PCM and a bad ground can look identical. Always check your main battery and engine grounds before replacing the module. It’s a 10-minute check that can save you a lot of headaches.
Common Symptoms of a Failing PCM
If the computer controlling your engine and transmission isn’t working correctly, you’ll notice. Keep an eye out for these common warning signs. A failing 2004 Blazer S10 PCM can be the root cause.
- ✔ Unexplained Check Engine Light illumination
- ✔ Stored diagnostic trouble codes (DTCs) like P0601, P0602, or P0606
- ✔ Vehicle refuses to start or cranks without firing
- ✔ Harsh or erratic automatic transmission shifting
- ✔ A significant, sudden drop in fuel economy
- ✔ Engine stalling, sputtering, or misfiring
- ✔ Failure to pass an emissions test
DIY Installation Guide for Your S10/Jimmy
Replacing the PCM on your Blazer or Jimmy is a straightforward job you can do in your driveway. The module is conveniently located in the right-hand front of the engine compartment. Follow these steps for a successful installation.
- Safety First: Always disconnect the negative terminal from your vehicle’s battery and wait at least 15 minutes for the system capacitors to discharge.
- Locate the PCM: Open the hood and find the PCM on the passenger side of the engine bay, typically near the firewall or inner fender.
- Disconnect the Harnesses: The PCM will have several large electrical connectors. Carefully lift the locking tabs or levers and gently pull the connectors straight out. Never force them. Inspect the pins for any corrosion or damage.
- Remove the Old Module: Unbolt the mounting bracket holding the old PCM in place. Keep the hardware as you will reuse it.
- Install the New PCM: Mount your new, pre-programmed module using the original hardware. Ensure it is secure.
- Reconnect Everything: Firmly plug the electrical harnesses back into the new PCM until they click into place. Reconnect the negative battery terminal.
- Security Relearn: In many cases, you will need to perform a security relearn procedure (often called a CASE learn) to sync the new PCM with your vehicle’s anti-theft system. 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.
Verified Vehicle Compatibility
This module, part number 12586243 (also replaces 89017739), is a direct fit for a wide range of 2004 GM vehicles. We program it specifically for your VIN. Please confirm your vehicle is on this list:
- ASTRO 04 (LH front by battery)
- AVALANCHE 2500 04 (LH front under battery)
- BLAZER S10/JIMMY S15 04 (RH front engine compartment)
- CORVETTE 04 (RH engine compartment, ID 12586243)
- CTS 04-05 (V-Series, RH engine compartment, ID 12586243)
- ENVOY XL / XUV 04 (5.3L, next to air box)
- EXPRESS 1500/2500/3500 VAN 04 (LH rear engine compartment)
- GTO 04 (main, LH engine)
- RAINIER 04 (5.3L, next to air box)
- SAFARI (GMC) 04 (LH front by battery)
- SAVANA 1500/2500/3500 VAN 04 (LH rear engine compartment)
- SIERRA 1500 PICKUP 04 (4.3L, LH front under battery)
- SIERRA 2500/3500 PICKUP 04 (Gasoline 8.1L, LH front under battery)
- SILVERADO 1500 PICKUP 04 (4.3L, LH front under battery)
- SILVERADO 2500/3500 PICKUP 04 (Gasoline 8.1L, LH front under battery)
- S10/S15/SONOMA 04 (RH front engine compartment)
- SSR 04 (next to air box)
- SUBURBAN 2500 04 (8.1L, LH front under battery)
- TRAILBLAZER EXT 04 (5.3L, next to air box)
- YUKON XL 2500 04 (8.1L, LH front under battery)
Frequently Asked Questions
Why do you need my VIN?
Your Vehicle Identification Number (VIN) allows us to program the PCM with the exact software and calibrations your 2004 Blazer S10 came with from the factory, including any performance and emissions updates from GM. This ensures perfect compatibility with your engine, transmission, and options.
Is this a plug-and-play part?
Almost! Because we pre-program it to your VIN, it eliminates the need for dealer-level programming tools. However, you will likely need to perform a simple security relearn procedure with your key, which takes about 30 minutes and requires no special tools. We provide instructions for this.
Will this fix my transmission shifting problems?
In many cases, yes. The PCM also controls transmission functions like shift points and line pressure. If the module is faulty, it can cause hard shifting, slipping, or delayed engagement. Replacing a bad PCM often resolves these issues.
Do I need to return my old PCM?
This listing does not require a core return. You can keep your old part, which can be helpful if you want to have it analyzed or simply don’t want the hassle of shipping it back.
What if my part number is 89017739?
This module, 12586243, is the correct, updated replacement for service part number 89017739. It is fully compatible and contains the most current software available.