Restore Peak Performance to Your GM Vehicle
Is your 2004-2005 Pontiac Bonneville, Cadillac DeVille, or Seville running poorly, stalling, or showing persistent check engine lights? The Engine Control Module (ECM), the central computer of your vehicle, is often the source of these frustrating and complex issues. This genuine, used OEM ECM, part number 12586547, is the reliable and cost-effective solution to get your vehicle back on the road. We take the guesswork out of the repair by programming the module specifically to your vehicle’s VIN before it ships, ensuring a seamless installation process.
Is Your 2004-2005 Bonneville ECM Failing?
A faulty engine computer can manifest in numerous ways, often mimicking other sensor or component failures. Proper diagnosis is key, but if you’re experiencing any of the following, a failing ECM is a likely suspect:
- ✔ Persistent Check Engine Light (CEL) with various communication or processor-related codes.
- ✔ Unexplained stalling or engine shutting off while driving.
- ✔ Rough idling, misfires, or hesitation during acceleration.
- ✔ Noticeable decrease in fuel economy.
- ✔ Harsh or erratic automatic transmission shifting.
- ✔ Complete no-start condition where the engine cranks but won’t fire up.
- ✔ Intermittent electrical issues that seem to have no other cause.
From the Diagnostic Bay
We had a 2004 Cadillac DeVille come into the shop with a maddening intermittent stalling problem. The owner had already replaced the crank and cam sensors, but the car would still randomly die at stoplights. After hours of checking wiring diagrams and testing circuits, we connected a scope to the ECM’s main processor. We found the voltage would sporadically drop, indicating an internal failure. We installed one of our pre-programmed used ECMs, performed the quick security relearn, and the car ran perfectly. It’s a classic case where the vehicle’s ‘brain’ was the hidden culprit all along.
A Plug-and-Play Solution Programmed for You
Don’t waste time and money at a dealership with a new, expensive module and additional programming fees. This unit is a direct replacement for service numbers 12587465, 12586547, and 15576920. The most critical step is already done for you. Upon purchase, simply provide us with your vehicle’s 17-digit VIN. Our technicians will then flash the module with the latest GM-certified software specific to your car’s configuration. This ensures all systems, from the engine and transmission to the anti-theft system, communicate correctly from the moment you plug it in.
Installation and Compatibility
The ECM is located in the left-hand (driver’s side) engine compartment. Installation is straightforward:
- Disconnect the Battery: Always disconnect the negative battery terminal before working on any electronic components.
- Locate and Unplug: Carefully unplug the wiring harnesses from the old ECM.
- Swap the Module: Unbolt the old module and bolt the replacement unit in its place.
- Reconnect: Securely plug the wiring harnesses into the new ECM and reconnect the battery.
- Perform Security Relearn: In most cases, you will need to perform a simple security relearn procedure. 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.
This part is a guaranteed fit for the following vehicles:
- 2004-2005 Pontiac Bonneville (with 4.6L engine)
- 2005 Cadillac DeVille (with matching ID 12587465)
- 2004 Cadillac DeVille
- 2004 Cadillac Seville
Frequently Asked Questions
Do I need to get this ECM programmed?
No. We handle the programming for you before we ship the part. You must provide your vehicle’s 17-digit VIN during or after checkout so we can load the correct software for your specific car.
What is a security relearn procedure?
A security relearn, or anti-theft relearn, is a simple process that syncs the new ECM to your car’s existing keys and security system. It usually involves a sequence of key turns and waiting periods and does not require any special tools. Instructions are widely available online for your specific model.
Is this a new part?
No, this is a high-quality, tested, and fully functional used OEM part sourced from a salvaged vehicle. This provides OEM reliability at a fraction of the cost of a new unit.
Where is the ECM located on my 2004 Bonneville?
The Electronic Control Module is located in the engine compartment on the driver’s side (LH side), typically near the fender or firewall.
Will this fix my car’s problem for sure?
This part will resolve any issues directly caused by a failing ECM. However, it is crucial that your vehicle has been properly diagnosed. This module will not fix problems related to other faulty sensors, wiring, or mechanical components.