If you’re dealing with frustrating engine problems in your GM truck or van—like intermittent stalling, a no-start condition, or a persistent check engine light—a failing Powertrain Control Module (PCM) is often the culprit. As the central computer of your vehicle, the PCM controls everything from fuel mixture and ignition timing to transmission shift points. When it fails, it can cause a host of issues that are difficult to diagnose. This is a reliable, tested, used OEM PCM, part number 9355699, that offers a direct solution.
The biggest hurdle with replacing a PCM has always been the expensive and time-consuming programming required at a dealership. We eliminate that step. Before we ship this module, we will flash it with the latest official GM software updates, specifically programmed to your vehicle’s unique VIN. This ensures that it’s a true plug-and-play solution, restoring your vehicle’s performance, reliability, and fuel efficiency without the extra cost or hassle.
Common Signs of a Failing GM PCM
- ✔ Your vehicle won’t start, or it starts and immediately stalls.
- ✔ The check engine light is on, and you have PCM-related diagnostic trouble codes (DTCs) like P0601, P0605, or P0606.
- ✔ You’re experiencing poor or erratic automatic transmission shifting.
- ✔ A noticeable drop in fuel economy for no apparent reason.
- ✔ The engine misfires, runs rough, or hesitates during acceleration.
- ✔ Loss of communication with the scan tool, making diagnostics impossible.
Case Study: The Ghost in the Machine
I had a 1999 Chevy Suburban come into the bay that was driving the owner crazy. It would randomly fail to start, but only after it was warm. He’d already replaced the fuel pump and crank sensor at another shop. We checked all the basics—fuel pressure, spark, and power/grounds to the PCM—and everything looked perfect. On a hunch, I monitored the 5-volt reference signal from the PCM while tapping on the module with a screwdriver handle. Sure enough, the signal would drop out, killing the engine. A faulty internal processor was the culprit. We installed one of these VIN-programmed PCMs, performed the quick security relearn, and the truck has been running perfectly ever since. Sometimes, the simplest solution is the right one.
A Straightforward Guide to Installation
Installing your new 1998-1999 GMC 3500 PCM is a job most DIYers can handle in under an hour with basic hand tools. This module is typically located in the engine compartment on the driver’s side.
- Safety First: Always disconnect the negative terminal from your vehicle’s battery before starting any electrical work.
- Locate the PCM: On most of these trucks and vans, you’ll find it mounted to a bracket in the engine bay, near the firewall or inner fender.
- Disconnect the Connectors: Carefully unlatch and remove the electrical harness connectors from the old PCM. Inspect them for any corrosion or damage.
- Remove the Old Module: Unbolt the old PCM from its mounting bracket and set it aside.
- Install the New PCM: Mount your new, pre-programmed PCM onto the bracket and securely fasten it.
- Reconnect Everything: Plug the electrical connectors firmly into the new module until they click into place. Reconnect the negative battery terminal.
- Perform Security Relearn (If Necessary): In most cases, you’ll need to perform a simple key-cycle security relearn procedure. Turn the key to the ‘ON’ position for 10-15 minutes, then ‘OFF’ for 10 seconds. Repeat this two more times. On the fourth try, the vehicle should start and run.
Verified Fitment Across the GM Lineup
While this is the correct computer for your 1998-1999 GMC 3500 PCM replacement, its versatility is a testament to GM’s platform sharing. This module, identified by service number 9355699 (or compatible numbers like 16266645 and 16250279), is a direct-fit for a wide range of popular 1998 and 1999 General Motors vehicles equipped with gasoline engines. This includes, but is not limited to:
- ✔ Chevrolet & GMC C/K 1500, 2500, & 3500 Pickups
- ✔ Chevrolet Tahoe & GMC Yukon
- ✔ Chevrolet & GMC Suburban
- ✔ Chevrolet Express & GMC Savana Vans (1500, 2500, 3500)
- ✔ Cadillac Escalade
- ✔ Chevrolet Astro & GMC Safari
- ✔ Oldsmobile Bravada, Chevrolet Blazer S10, GMC Jimmy S15/Envoy, & Isuzu Hombre (4.3L V6 models)
To guarantee a perfect match, please provide your VIN upon purchase. This allows us to ensure the programming is 100% correct for your vehicle’s specific options and configuration.
Frequently Asked Questions
Why do you need my VIN?
Your Vehicle Identification Number (VIN) is essential. It allows us to access the exact factory software and calibrations for your specific truck, including engine size, transmission type, and emissions equipment. This ensures the PCM works seamlessly with your vehicle right out of the box.
Is any additional programming needed after installation?
No. This PCM arrives pre-programmed and ready for installation. The only step you may need to perform is a simple security relearn procedure, which involves a series of key cycles and does not require any special tools.
What happens if I don’t replace a failing PCM?
Ignoring a failing PCM can lead to more severe problems, including catalytic converter damage from an incorrect fuel mixture, unpredictable stalling in traffic, and eventually, a complete no-start condition that will leave you stranded.
Is this a used part?
Yes, this is a thoroughly tested and inspected used OEM part sourced from a salvaged vehicle. This provides OEM reliability and function at a fraction of the cost of a new module from the dealer.
Will this fix my specific problem?
This module will correct issues directly caused by a faulty PCM. While the symptoms listed are common indicators, it’s always best practice to have a proper diagnosis performed to rule out other potential causes like bad sensors or wiring issues before ordering.