Is Your Late 90s GM Truck or SUV Running Rough?
If you’re dealing with a frustrating no-start condition, a persistent check engine light, erratic engine behavior, or poor fuel mileage in your 1998-1999 GM vehicle, a failing Powertrain Control Module (PCM) is a very common culprit. The PCM is the central computer, the ‘brain’ of your vehicle’s engine and transmission. It controls everything from fuel injection and spark timing to transmission shift points. When it starts to fail, it can cause a wide range of confusing and difficult-to-diagnose problems, leaving your reliable truck or SUV dead in the driveway.
The Brain of Your Vehicle: What the PCM Does
The PCM in your GMT400 or S-series platform vehicle is a critical component. It constantly analyzes data from dozens of sensors throughout the engine and drivetrain. It reads throttle position, engine RPM, coolant temperature, oxygen sensor data, and much more. Based on this information, it makes instantaneous decisions to keep the engine running efficiently and smoothly. A faulty module can misinterpret this data or fail to send the correct commands, leading to the symptoms you’re experiencing.
From the Diagnostic Bay
We had a 1999 Suburban come in that the owner had spent a fortune on. It had an intermittent stalling issue that no one could figure out. He had replaced the fuel pump, crank sensor, ignition coil, and a handful of other parts. The truck would run fine for a week, then stall at a stoplight and refuse to restart for an hour. After checking all the wiring and grounds, we hooked up a scope to the injector command signal from the PCM. We found that the signal would randomly drop out completely, starving the engine of fuel. A replacement PCM, programmed to the VIN, solved the problem instantly. It’s a classic case of a failing computer mimicking other component failures.
Symptoms of a Failing GM PCM
- ✔ Check Engine Light: Often, you’ll see codes related to internal module failure, memory errors, or communication loss (U-codes).
- ✔ No-Start or Intermittent Start: The engine cranks but won’t fire up because the PCM isn’t commanding fuel or spark.
- ✔ Poor Engine Performance: Stalling, rough idling, hesitation, and a noticeable loss of power are common signs.
- ✔ Harsh or Erratic Shifting: The PCM also controls the transmission, and a failure can lead to hard shifts, getting stuck in a gear, or delayed engagement.
- ✔ Decreased Fuel Economy: When the PCM can’t properly manage the engine’s fuel mixture, your gas mileage will suffer significantly.
- ✔ Failure to Pass Emissions: A faulty PCM will prevent the vehicle’s emissions systems from operating correctly, resulting in a failed test.
Your Direct-Fit Solution: The 1998-1999 Yukon PCM
This is a genuine, used OEM Powertrain Control Module, part number 09355699, that has been tested for full functionality. We eliminate the guesswork and high dealership costs by programming the module specifically for your vehicle before it ships. Simply provide us with your vehicle’s 17-digit VIN (Vehicle Identification Number) during or after checkout, and we will flash the unit with the latest, most up-to-date software from General Motors. This ensures that the module is a direct, plug-and-play replacement for your original, faulty unit.
Installation and Relearn Procedure
Physically installing the module is straightforward. Disconnect the negative battery terminal, locate your existing PCM in the engine bay, carefully unplug the wiring harnesses, and swap the module. After reconnecting the battery, you will need to perform a security relearn procedure, also known as a CASE (Crankshaft Angle Sensor Error) relearn. This procedure syncs the new PCM with your vehicle’s anti-theft system and crankshaft position sensor. This can often be done without special tools and instructions can be found online, or your mechanic can perform it quickly with a capable scan tool.
Guaranteed Fitment for Part Number 09355699
This module is a direct replacement for service numbers 09355699, 16266645, 9355699, 16250279, 16258815, 09366810, and 9366810. Please verify that your current module has one of these numbers printed on the label to ensure compatibility. This part fits a wide range of GM vehicles, including:
- Cadillac Escalade (1999)
- Chevrolet Astro / GMC Safari (1998)
- Chevrolet Blazer / GMC Jimmy S15 / Oldsmobile Bravada (1998)
- Chevrolet & GMC C/K 1500, 2500, 3500 Pickups (1998-1999)
- Chevrolet & GMC Suburban 1500, 2500 (1998-1999)
- Chevrolet Tahoe / GMC Yukon (1998-1999)
- Chevrolet Express / GMC Savana 1500, 2500, 3500 Vans (1998-1999)
- GMC Envoy (1998)
- Isuzu Hombre (1998)
- Chevrolet S10 / GMC Sonoma (1998)
Frequently Asked Questions
How do I provide my VIN for programming?
You can add your 17-digit VIN to the notes section during checkout, or simply reply to our order confirmation email. We cannot ship the module until we have your VIN to program it.
Is this a new part?
No, this is a thoroughly tested, fully functional used OEM part sourced from a salvaged vehicle. This provides OEM reliability without the high cost of a new module.
Do I need to do anything after installing this PCM?
Yes. After installation, you must perform a security relearn and a CASE relearn. This is a required step to sync the module to your vehicle’s anti-theft system and crankshaft sensor. Your mechanic can do this, or you can find vehicle-specific instructions online.
Will this fix my vehicle’s problem?
This module will resolve any issues directly caused by a faulty PCM. However, it’s crucial that your vehicle has been properly diagnosed. This part will not fix problems related to bad sensors, wiring, or other mechanical failures.
What is the difference between a PCM and an ECM?
For these vehicles, the terms are often used interchangeably. PCM (Powertrain Control Module) is technically more accurate as it controls both the engine (Engine Control Module – ECM) and the transmission (Transmission Control Module – TCM) functions within a single unit.