Programmed 2004 Rainier PCM 12586243 | VIN-Matched Engine Computer ECM

Restore Your GM’s Performance and Reliability

Is your 2004 Buick Rainier or other GM vehicle acting up? Frustrating issues like a persistent check engine light, unexplained stalling, poor fuel economy, or harsh shifting can often be traced back to one single component: a failing Powertrain Control Module (PCM). As a technician with over two decades of experience, I’ve seen firsthand how a faulty PCM can create a cascade of problems that are difficult to diagnose. It’s the brain of your vehicle, and when it’s not working correctly, nothing else will either.

This isn’t just a replacement part; it’s a direct solution. We are providing a dependable Electronic Control Module (ECM), also known as a PCM, that is specifically programmed to your vehicle’s unique Vehicle Identification Number (VIN). This critical step ensures that the module communicates perfectly with your engine, transmission, and all other onboard systems. We flash it with the latest GM-certified software updates, which can often resolve performance issues that were present even before the original module failed. Forget the expensive trip to the dealership for programming—this module arrives ready for installation.

Common Signs of a Failing PCM

• ✔ Your vehicle fails to start or starts intermittently.
• ✔ The check engine light is on with internal processor codes like P0601, P0602, or P0606.
• ✔ Unexplained drops in fuel efficiency.
• ✔ The engine stalls, sputters, or misfires for no apparent reason.
• ✔ Erratic or delayed automatic transmission shifting.
• ✔ Failure to pass state emissions testing.

A Straightforward Guide to Installation

Replacing the PCM on these GM vehicles is a job most DIYers can handle with basic tools. The key is patience and following the correct procedure. While locations vary slightly by model, the process is generally the same.

1. Safety First: Disconnect the negative terminal from your vehicle’s battery and secure it away from the post to prevent any accidental reconnection.
2. Locate the PCM: On the 2004 Rainier, Envoy, and Trailblazer models, it’s typically located in the engine bay, next to the air filter box. On trucks and vans, it’s often found under the battery tray on the driver’s side.
3. Disconnect the Connectors: Carefully unlatch and remove the electrical wiring harness connectors from the old PCM. These connectors have locking tabs; do not force them. Inspect the pins for any corrosion or damage.
4. Remove the Old Module: Unbolt the PCM from its mounting bracket. It’s usually held in place by a few small bolts or nuts.
5. Install the New Module: Mount your new, VIN-programmed PCM onto the bracket and securely fasten it.
6. Reconnect Everything: Plug the wiring harnesses back into the new module until they click firmly into place. Reconnect the negative battery terminal.
7. Perform Security Relearn (If Needed): In most cases, a simple security relearn procedure is required. Turn the key to the ‘ON’ position for 10-15 minutes, then ‘OFF’ for 10 seconds. Repeat this cycle three times. This allows the new PCM to synchronize with your vehicle’s anti-theft system. On the fourth cycle, the vehicle should start.

Verified Vehicle Compatibility

This module, part number 12586243 (also interchangeable with 89017739), is a direct fit for a wide range of 2004 and some 2005 GM vehicles. Please confirm your part number and specific model options. This is a partial list of compatible models:

• ✔ 2004 Buick Rainier (5.3L)
• ✔ 2004 Cadillac CTS-V
• ✔ 2004 Chevrolet Avalanche, Silverado, Suburban & Tahoe (Gasoline Engines)
• ✔ 2004 Chevrolet Corvette
• ✔ 2004 Chevrolet Express Van
• ✔ 2004 Chevrolet SSR
• ✔ 2004 Chevrolet S10 / Blazer
• ✔ 2004 Chevrolet Trailblazer EXT (5.3L)
• ✔ 2004 GMC Envoy XL / XUV (5.3L)
• ✔ 2004 GMC Sierra, Yukon & Yukon XL (Gasoline Engines)
• ✔ 2004 GMC Savana Van
• ✔ 2004 GMC Sonoma / Jimmy
• ✔ 2004 Pontiac GTO