Is your 1998 or 1999 GMC 3500 pickup running rough, stalling, or showing a persistent check engine light? These are classic signs of a failing Powertrain Control Module (PCM), the central computer that manages your truck’s engine and transmission performance. A faulty PCM can lead to a cascade of frustrating issues, from poor fuel economy and failed emissions tests to a vehicle that won’t start at all. This genuine OEM PCM, part number 9355699, is the reliable, plug-and-play solution to restore your truck’s performance and dependability.
From the Diagnostic Bay
We had a ’99 Chevy Suburban come in that was driving the owner crazy. It would randomly stall at stoplights, the transmission would shift hard, and the check engine light was on with a handful of seemingly unrelated codes. The owner had already replaced the spark plugs, wires, and even the fuel pump with no success. After hooking up our diagnostic scanner and monitoring live data, we noticed erratic sensor readings that didn’t make sense. The voltage references were fluctuating slightly. This pointed us directly to the PCM. We installed a VIN-programmed module just like this one, performed the security relearn, and the truck ran like it just rolled off the factory floor. All the ghost codes vanished, and the hard shifting was gone. It’s a reminder that sometimes the root cause is the brain, not the body.
Common Symptoms of a Failing 1998-1999 GMC 3500 PCM
- ✔ Persistent Check Engine Light (CEL) with various trouble codes.
- ✔ Engine stalling, stumbling, or misfiring.
- ✔ Harsh or erratic automatic transmission shifting.
- ✔ Noticeable decrease in fuel economy.
- ✔ The engine cranks but fails to start.
- ✔ Failure to communicate with diagnostic scan tools.
- ✔ Inconsistent performance that gets worse as the engine warms up.
The Brain of Your Operation
The PCM is the undisputed command center of your vehicle. It takes in data from dozens of sensors—like the oxygen sensors, crankshaft position sensor, and throttle position sensor—and uses this information to make millions of calculations per second. It controls fuel injection timing, spark advance, transmission shift points, and emissions systems to ensure your engine runs efficiently and powerfully. When the internal circuits of the PCM begin to fail due to age, heat, or vibration, these critical calculations become corrupted, leading to the symptoms you’re experiencing.
Plug-and-Play Solution, Programmed for Your Truck
Replacing a PCM isn’t as simple as swapping a battery. Modern vehicle computers are coded specifically to the Vehicle Identification Number (VIN) of the truck they are installed in. This ensures all systems, including anti-theft and specific engine calibrations, work correctly. Our service eliminates the guesswork and the need for expensive dealership programming. When you purchase this module, simply provide us with your truck’s VIN. We will flash the unit with the latest GM-certified software updates specific to your vehicle. When it arrives, it’s ready to be installed, making this a true plug-and-play repair.
OEM Quality and Broad Compatibility
This is a used, genuine OEM computer sourced from a salvaged vehicle, ensuring perfect fitment and factory-level reliability. It is a direct replacement for several part numbers, including: 09355699, 16266645, 16250279, 16258815, 09366810, and 9366810. While this listing is focused on the 1998-1999 GMC 3500 PCM, this versatile module also fits a wide range of other GM trucks, vans, and SUVs from that era. Please verify your original part number and consult the detailed fitment list to confirm compatibility with your specific vehicle.
Frequently Asked Questions
Do I need to get this PCM programmed?
No. This PCM comes pre-programmed to your vehicle’s specific VIN. After you place your order, you will need to provide us with your VIN so we can flash the module with the correct GM software before shipping. This makes the installation process much simpler.
Where is the PCM located on my 1998-1999 GM truck?
On most full-size GM trucks and SUVs from this era, including the GMC 3500, the PCM is located in the engine compartment, typically on the driver’s side inner fender or near the firewall.
What is a security or CASE relearn procedure?
After installing the new PCM, your vehicle’s anti-theft system (Passlock/VATS) may need to be synchronized with the new module. This is a simple procedure that usually involves turning the key to the ‘ON’ position for 10-15 minutes, then off, and repeating two more times. A Crankshaft Variation Relearn (CASE) may also be needed with a capable scan tool to prevent a P1336 trouble code, but the vehicle will run and drive without it.
Is this a new part?
This is a high-quality, tested, used OEM part that has been sourced from a salvaged vehicle. Using a genuine OEM part ensures the highest level of compatibility and reliability for your vehicle.
How do I find my vehicle’s VIN?
Your 17-digit VIN can be found on your vehicle’s registration, insurance card, or on a metal plate on the driver’s side of the dashboard, visible through the windshield.