Is Your GM Truck Running Rough? The PCM Might Be the Culprit.
If your 1998-1999 GMC 3500, Chevrolet truck, or van is experiencing perplexing issues like stalling, poor fuel economy, erratic shifting, or a persistent check engine light, you may be dealing with a failing Powertrain Control Module (PCM). As the central computer of your vehicle, the PCM is responsible for managing everything from fuel injection and ignition timing to transmission shift points. When it starts to fail, it can cause a cascade of problems that are often misdiagnosed, leading to costly and unnecessary repairs of other components.
This isn’t just a replacement part; it’s a direct solution. We offer a genuine, used OEM Powertrain Control Module, service number 9355699, that is meticulously tested and ready for installation. The key to our service is that we program the module specifically for your vehicle using your VIN. This means it arrives loaded with the latest GM factory software updates, ensuring optimal performance and compatibility right out of the box. You get a reliable, cost-effective repair without the exorbitant costs and scheduling hassles of a dealership visit.
From the Diagnostic Bay
I remember a customer with a ’99 Chevy Suburban who had spent months chasing a ghost. The truck would randomly die at stoplights and had a strange hesitation under acceleration. He had replaced the fuel pump, ignition coil, and a handful of sensors, but the problem persisted. When he finally brought it to our shop, we connected our diagnostic scanner and saw erratic data from multiple sensors that didn’t make sense together. That’s a classic sign of a failing computer. Instead of throwing more parts at it, we identified the PCM as the root cause. We installed a VIN-programmed module just like this one, and the truck ran like it was new. It’s a powerful reminder that sometimes the problem lies with the ‘brain,’ not the ‘body’ of the engine.
Diagnosing a Failing 1998-1999 GMC 3500 PCM
The PCM in these GMT400 and early GMT800-era trucks is a known failure point after decades of heat cycles and vibrations. Symptoms can be intermittent at first, making diagnosis tricky. If your vehicle is showing any of the following signs, a faulty PCM should be a primary suspect.
Common Symptoms of a Bad PCM
- ✔ Check Engine Light: The light may be on with codes related to multiple, unrelated sensors, or internal processor failure codes.
- ✔ No-Start or Hard-Start Condition: The engine may crank but fail to start, or take an unusually long time to fire up, especially when warm.
- ✔ Poor Engine Performance: Noticeable loss of power, rough idling, stalling, engine hesitation, or misfires.
- ✔ Decreased Fuel Economy: A failing PCM can’t efficiently manage the engine’s fuel delivery, leading to a sudden drop in MPG.
- ✔ Harsh or Erratic Shifting: The PCM also controls the transmission. You might experience delayed shifting, hard shifts, or getting stuck in one gear.
- ✔ Communication Issues: Your OBD-II scanner may be unable to communicate with the vehicle’s computer.
The Simple, Plug-and-Play Solution
Don’t let a bad computer keep your reliable truck off the road. Our process is designed to be as straightforward as possible. After you place your order, simply provide us with your vehicle’s 17-digit VIN. Our technicians will use this to flash the module with the correct, updated software for your specific make, model, engine, and transmission. This ensures all parameters are set correctly for your vehicle’s configuration. The module you receive will be a direct, plug-and-play replacement. In most cases, a simple security relearn procedure (which can be done without special tools) is all that’s needed to get you back on the road.
This module is compatible with a wide range of GM trucks, vans, and SUVs from 1998-1999. Please verify your original part number matches 9355699 or one of the alternate numbers (16266645, 16250279, 16258815, 09366810) and consult the detailed fitment list to confirm compatibility.
Frequently Asked Questions
Do I need to get this computer programmed?
No. This computer comes fully programmed to your vehicle’s specific VIN. We handle all the flashing and software updates before it ships, so it’s ready for installation when you receive it.
Is this a new part?
This is a high-quality, used OEM part sourced from a salvaged vehicle. Each unit is thoroughly inspected and tested to ensure it meets factory performance standards before being programmed and shipped.
What is a VIN and why do you need it?
The VIN (Vehicle Identification Number) is a unique 17-digit code for your vehicle. We use it to access the specific factory software and calibrations for your truck’s engine, transmission, and options, ensuring the PCM works perfectly.
Will this fix my check engine light?
If the check engine light is caused by an internal failure of your old PCM, then yes, this part will resolve the issue. However, if the light is on due to a separate faulty sensor or mechanical problem, that issue will still need to be addressed.
What is a security relearn procedure?
On many GM vehicles of this era, the PCM is tied to the anti-theft system (Passlock/VATS). After installing the new PCM, you may need to perform a simple procedure, typically involving turning the key on and off in a specific sequence, to allow the new computer to sync with your vehicle’s security system. Instructions are widely available online for this process.