Restore Peak Performance to Your GM Truck or Van
If you’re dealing with frustrating issues like a persistent check engine light, erratic engine behavior, or a no-start condition in your 2003 Chevy Blazer S10 or GMC Jimmy S15, a failing Powertrain Control Module (PCM) is often the culprit. As the central computer of your vehicle, the PCM controls everything from fuel mixture and ignition timing to transmission shifting. When it fails, the symptoms can be unpredictable and difficult to diagnose. This module, part number 12570557, is the definitive solution to get your truck running reliably again.
The biggest hurdle in replacing a PCM has always been the programming. Dealerships charge a premium for this service, and it requires specialized equipment. We’ve eliminated that barrier. Before we ship this module, we will flash it with the latest official GM software updates, precisely matched to your vehicle’s VIN. This means it arrives at your door ready for installation, saving you time, money, and a trip to the dealer. It’s the most straightforward way to restore your vehicle’s original performance and efficiency.
Case Study: The Ghost Misfire
A 2003 GMC Sonoma with the 4.3L V6 came into my shop with a maddening problem: a random misfire on cylinder 3 (P0303) that only happened under light acceleration. The owner had already replaced the plug, wire, cap, rotor, and even the fuel injector. Everything tested fine. After hours of chasing my tail, I hooked up a lab scope to the PCM’s injector driver for cylinder 3. The signal was weak and erratic. The internal driver in the original PCM was failing intermittently under load. We installed a VIN-programmed module just like this one, and the misfire was gone for good. Sometimes, the problem really is the computer.
Is Your GM Truck Showing These Symptoms?
A faulty PCM can manifest in many ways. If you’re experiencing any of the following, this module is likely the solution you need. In my 20+ years of diagnostics, these are the most common indicators of a failing computer.
- ✔ Vehicle refuses to start or stalls unexpectedly.
- ✔ Harsh or erratic automatic transmission shifting.
- ✔ A significant, unexplained drop in fuel economy.
- ✔ Check Engine Light is on with codes like P0601, P0602, P0606 (Internal Control Module Processor Error).
- ✔ Communication errors with other modules (U-codes).
- ✔ Engine misfires or runs rough after all ignition and fuel components have been checked.
- ✔ Failure to pass an emissions test.
A Straightforward Guide to Installation
Installing your new 2003 Blazer S10 PCM is a manageable job for a confident DIYer. The key is the security relearn procedure, which is simple but must be followed correctly. This allows your vehicle’s anti-theft system to recognize the new module.
- Safety First: Disconnect the negative terminal from your vehicle’s battery.
- Locate the PCM: On the Blazer/Jimmy/S10, it’s typically located in the engine compartment on the passenger’s side, near the firewall or fender.
- Disconnect and Remove: Carefully unplug the wiring harness connectors. They have locking tabs that need to be released. Then, unbolt the module from its mounting bracket.
- Install the New Module: Bolt the new PCM into place and securely reconnect all wiring harnesses. Ensure they click into place. Reconnect the battery terminal.
- Perform Security Relearn (CRITICAL): Do NOT attempt to start the engine yet. Turn the key to the ‘ON’ position (don’t crank). Leave it on for 10-12 minutes, or until the ‘Security’ light on the dash turns off. Turn the key ‘OFF’ for 10 seconds. Repeat this cycle two more times (for a total of three 10-minute cycles). The vehicle should now start and run normally.
Verified Vehicle Compatibility
This module is a direct replacement for a wide range of GM vehicles. Please confirm your model and options below. This unit replaces service numbers: 12581565, 8125815650, 12570557, 12570558, 12576106, 12576869, 12578127, 88864822, and 89017733.
- ASTRO 03: Electronic Control Module; (LH front by battery)
- AVALANCHE 2500 03: Electronic Control Module; (LH front under battery)
- BLAZER S10/JIMMY S15 03: Electronic Control Module; (RH front engine compartment)
- CTS 04: Electronic Control Module; (RH engine compartment), Base, ID 12581565
- CORVETTE 04: Electronic Control Module; (RH engine compartment), ID 12581565
- EXPRESS/SAVANA 1500/2500/3500 VAN 03: Electronic Control Module; (LH rear engine compartment)
- S10/S15/SONOMA 03: Electronic Control Module; (RH front engine compartment), 4.3L
- SAFARI (GMC) 03: Electronic Control Module; (LH front by battery)
- SIERRA 1500 PICKUP 03: Electronic Control Module; (LH front under battery), w/4.3L
- SIERRA/SILVERADO 2500/3500 PICKUP 03: Electronic Control Module; (LH front under battery), gasoline, 8.1L
- SUBURBAN 2500 03: Electronic Control Module; (LH front under battery), 8.1L
- YUKON XL 2500 03: Electronic Control Module; (LH front under battery), 8.1L
Frequently Asked Questions
Do I really need to provide my VIN?
Yes, providing your 17-digit Vehicle Identification Number (VIN) is essential. We use it to load the correct, vehicle-specific GM software and calibrations onto your module before shipping. This ensures it works perfectly with your engine, transmission, and options.
What is the ‘Security Relearn’ and is it hard?
The security relearn (also known as a VATS or Passlock relearn) is a simple procedure that syncs the new PCM to your vehicle’s anti-theft system. It does not require any special tools, just your ignition key and about 30 minutes of time, as outlined in the installation steps. It is a mandatory step.
Will this fix my check engine light?
If the check engine light is caused by an internal PCM failure (like codes P0601-P0606) or a faulty component driver within the module, then yes, this will resolve the issue. However, if the light is on due to a separate faulty sensor or component on the vehicle, that part will still need to be addressed.
Is this a plug-and-play part?
Almost! Because it comes pre-programmed to your VIN, it’s as close to plug-and-play as you can get. The only additional step required after physical installation is the 30-minute security relearn procedure, which you can do yourself right in your driveway.
How do I find my PCM on a 2003 Blazer S10?
On the 2003 Blazer, S10, Jimmy, and Sonoma, the PCM is located in the engine bay on the right-hand (passenger) side, typically mounted to the inner fender or firewall area. It’s a silver metal box with several large wiring harness connectors.