Restore Peak Performance to Your Cadillac STS
Is your 2009-2010 Cadillac STS running rough, stalling unexpectedly, or showing a persistent Check Engine Light? These are classic signs of a failing Engine Control Module (ECM), the computer that acts as your vehicle’s brain. A faulty ECM can cripple performance, hurt fuel economy, and make your car unreliable. This isn’t just an inconvenience; it’s a problem that needs a definitive solution. As a technician with over two decades of experience, I’ve seen how a failing ECM can cause a cascade of frustrating, hard-to-diagnose issues.
This replacement Engine Control Module, part number 12639300, is the reliable, straightforward fix you need. We take the guesswork and hassle out of the repair by programming the module specifically for your vehicle using your VIN. This means it arrives at your door loaded with the latest GM factory software, ready for a plug-and-play installation. You get a component that restores original functionality without the expensive trip to the dealership for programming.
From the Diagnostic Bay: The Ghost in the Machine
I remember a 2009 Cadillac CTS-V that came into my shop with an intermittent no-start condition that was driving the owner crazy. It would be fine for days, then suddenly refuse to crank. There were no consistent trouble codes, just a frustrating U0100 (Lost Communication with ECM) that would pop up occasionally. We checked wiring, grounds, and the ignition system—all perfect. After hours of diagnostics, we found the culprit: the ECM itself. Internally, a solder joint was failing intermittently due to heat cycles. Replacing it with a pre-programmed unit like this one solved the problem instantly. It’s a reminder that sometimes the most complex issues have a simple, high-quality component solution.
Common Signs of a Failing Engine Computer
If you’re experiencing any of the following, a faulty ECM could be the root cause. A failing 2009-2010 STS ECM often triggers specific diagnostic trouble codes (DTCs) that can be read with a standard OBD-II scanner.
- ✔ Check Engine Light: The light is on, and you may have codes like P0601, P0606, or other processor faults.
- ✔ Engine Stalling or Misfiring: The engine may shut off while driving or run erratically.
- ✔ No-Start Condition: The engine cranks but refuses to start, or doesn’t crank at all.
- ✔ Poor Performance & Fuel Economy: A noticeable drop in power and an increase in fuel consumption.
- ✔ Communication Errors: Your scan tool cannot communicate with the ECM, often showing a U0100 code.
- ✔ Erratic Automatic Transmission Shifting: The ECM plays a key role in telling the transmission when to shift.
A Straightforward Guide to Installation
Replacing the ECM on your Cadillac STS is a manageable job for a DIYer with basic tools. Our VIN-programming service makes it even easier by eliminating the need for dealer-level software. For the 2009-2010 STS, the module is typically located on the left-hand (driver’s side) frame rail.
- 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: Find the Engine Control Module. On the STS, it’s mounted to the LH frame rail. You may need to remove a splash shield for access.
- Disconnect Connectors: Carefully unlatch and remove the electrical wiring harness connectors from the old module. Inspect them for any corrosion or damage.
- Remove the Old Module: Unbolt the old ECM from its mounting bracket.
- Install the New Module: Mount your new, pre-programmed ECM in place and securely fasten it.
- Reconnect Everything: Plug the wiring harnesses back into the new module until they click into place. Reconnect your battery terminal.
- Final Step: Your vehicle may require a security relearn procedure, which can typically be done without special tools by cycling the key. Instructions are widely available online or in service manuals.
Verified Vehicle Compatibility
This ECM is a direct replacement for a wide range of GM vehicles, ensuring broad compatibility. We guarantee it will function correctly if your vehicle is on this list and you provide a valid VIN for programming. This module is interchangeable with service numbers: 12636659, 12639300, 1263605, 12628993, 12628911, 12625453, 12622175, 12630464, and 12678512.
CADILLAC DTS 09-11
CADILLAC SRX 09 (4.6L)
CADILLAC STS 09 (4.4L or 4.6L)
CADILLAC STS 10 (4.6L)
CADILLAC XLR 09 (ID 12636659 or 12625453)
CHEVROLET COLORADO 09-12 (2.9L or 3.7L)
CHEVROLET CORVETTE 09 (ZR1)
CHEVROLET TRAILBLAZER 09 (6.0L)
GMC CANYON 09-12 (2.9L or 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 About the 2009-2010 STS ECM
Frequently Asked Questions
How do I provide my VIN number?
After you complete your purchase, you can add your 17-digit Vehicle Identification Number (VIN) in the notes section of your order or send it to us via email. We cannot program and ship the module without it.
Is this a simple plug-and-play installation?
Yes, for most vehicles on the fitment list. Because we program the module to your VIN, it eliminates the need for dealer programming. Some vehicles may require a simple key-cycle security relearn procedure, which does not require special tools.
Will this fix my specific problem?
This module will correct issues directly caused by a faulty ECM, such as internal processor errors (P0601), no-start conditions, and erratic engine behavior. It’s crucial to ensure your vehicle has been properly diagnosed, as other failing sensors or wiring issues can cause similar symptoms.
What if my original part number is not 12639300?
That’s okay. This ECM is a direct replacement for several service numbers, including 12636659, 12628993, 12625453, and others listed in the description. As long as your vehicle model and year are listed, this module will work once programmed.
Does this module come with a warranty?
Yes, all our modules come with a warranty that covers any defects in the component itself. Please refer to our warranty policy page for complete details and duration.