Restore Your Cadillac’s Performance and Reliability
Is your 2009-2010 Cadillac STS suffering from frustrating issues like a persistent check engine light, poor engine performance, stalling, or erratic shifting? These are classic signs of a failing Engine Control Module (ECM). As the brain of your vehicle, a faulty ECM can cause a cascade of problems that are often difficult to diagnose. This replacement ECM, part number 12639300, is the definitive solution to get your luxury sedan running smoothly again.
What sets this module apart is our professional programming service. Before we ship it, we flash the module with the latest GM-certified software updates, tailored specifically to your vehicle using your VIN. This means you receive a part that is truly ready for installation, eliminating the need for an expensive trip to the dealership for programming. It’s a direct-fit, effective solution for both professional mechanics and savvy DIY owners.
Common Signs of a Failing ECM
- ✔ Check Engine Light (CEL) is illuminated with codes like P0601, P0606, or U0100.
- ✔ The engine cranks but refuses to start.
- ✔ Unexplained drops in fuel economy.
- ✔ Noticeable loss of power and poor acceleration.
- ✔ The engine misfires, stalls, or runs rough intermittently.
- ✔ Automatic transmission shifts harshly or at the wrong times.
- ✔ Communication issues with diagnostic scan tools.
A Technician’s Notebook
I remember a 2009 Cadillac STS that came into my bay with a complaint of intermittent, harsh 2-3 shifts and a no-start condition when hot. The owner had already replaced the transmission fluid and solenoids with no luck. Scans showed no specific transmission codes, just a generic U-series communication code that would come and go. After checking all the wiring harnesses, I focused on the ECM. On these vehicles, heat soak can cause internal fractures in the ECM’s circuit board. We swapped in a properly programmed ECM, and both the shifting and hot-start problems vanished. It’s a great reminder that the ECM’s health is critical for the entire powertrain, not just the engine.
A Straightforward Guide to Installation
- ✔ Safety First: Disconnect the negative terminal from your vehicle’s battery and secure it away from the post to prevent accidental reconnection.
- ✔ Locate the ECM: On the 2009-2010 Cadillac STS, the ECM is typically located on the driver’s side frame rail, underneath the vehicle. Always confirm the location for your specific model before starting.
- ✔ Disconnect Connectors: Carefully release the locking tabs and unplug the wiring harness connectors from the old ECM. Inspect the connectors for any corrosion or damage.
- ✔ Remove the Old Module: Unbolt the mounting hardware that secures the old ECM to its bracket and remove it from the vehicle.
- ✔ Install the New Module: Mount your new, pre-programmed ECM in the same location and secure it with the original hardware.
- ✔ Reconnect and Finalize: Plug the wiring harnesses firmly into the new module until they click into place. Reconnect the negative battery terminal. The vehicle may require a security relearn procedure, which can often be done by cycling the key.
Verified Vehicle Compatibility
This module is a direct replacement for a wide range of GM vehicles and is interchangeable with part numbers 12636659, 12639300, 1263605, 12628993, and more. While this listing is focused on the 2009-2010 STS ECM, it also fits the following models. Please verify your specific engine and options.
CADILLAC DTS 09-11
CADILLAC SRX 09 (4.6L)
CADILLAC STS 09 (4.4L, 4.6L)
CADILLAC STS 10 (4.6L)
CADILLAC XLR 09
CHEVROLET COLORADO 09-12 (2.9L, 3.7L)
CHEVROLET CORVETTE 09 (ZR1)
CHEVROLET TRAILBLAZER 09 (6.0L)
GMC CANYON 09-12 (2.9L, 3.7L)
GMC ENVOY 09 (5.3L)
HUMMER H3 / H3T 09-10 (3.7L)
BUICK LUCERNE 09-11 (4.6L)
SAAB 9-7X 09
Frequently Asked Questions
Frequently Asked Questions
Do I need to do any programming after I receive this ECM?
No. We program the module to your vehicle’s specific VIN before shipping. It arrives ready for installation, with no extra dealer visits required.
How do I provide my VIN number?
Simply enter your 17-digit Vehicle Identification Number (VIN) in the designated box on the checkout page, or send it to us in a message after your purchase.
Where is the ECM located on my 2009 Cadillac STS?
The Engine Control Module on the 2009-2010 STS is mounted to the left-hand (driver’s side) frame rail. You will need to access it from underneath the vehicle.
Will this fix my check engine light?
If the check engine light is caused by a faulty ECM (e.g., internal processor failure codes like P0601), this part will resolve the issue. It’s essential to ensure the root cause of the problem is the ECM and not a separate sensor or wiring fault.
What if I have the wrong part number?
This module replaces a wide range of service numbers, including 12636659, 12628993, and 12625453. As long as your vehicle is on the compatibility list, this VIN-programmed module is the correct part for the job.