Is Your Workhorse GMC 3500 Suddenly Unreliable?
If you rely on your 1999-2000 GMC 3500, you know it’s built to handle tough jobs. But when the Powertrain Control Module (PCM) starts to fail, that dependable truck can become a major headache. As the electronic brain of your engine and transmission, a faulty PCM can cause a cascade of confusing and frustrating problems that can bring your work to a standstill.
Over my 20+ years turning wrenches, I’ve seen hundreds of these GMT400 and early GMT800 platform trucks come into the shop with PCM-related issues. The symptoms aren’t always straightforward, which can lead to misdiagnosis and wasted money on parts you don’t need.
Common Symptoms of a Failing GMC 3500 PCM
A failing engine computer can manifest in many ways. If you’re experiencing any of the following, your PCM is a likely culprit:
- โ Unexplained stalling, especially after the engine warms up.
- โ Harsh or erratic automatic transmission shifting.
- โ Complete no-start condition, where the engine cranks but won’t fire.
- โ Check Engine Light is on with multiple, seemingly unrelated diagnostic trouble codes (DTCs).
- โ Poor fuel economy and a noticeable loss of power.
- โ Intermittent issues that disappear and then return without warning.
- โ Your scan tool cannot communicate with the PCM at all.
Expert Pro Tip: Check Your Grounds First!
Before you condemn your PCM, do yourself a favor and check the basics. On these GM trucks, a corroded or loose ground strap can cause voltage issues that mimic a bad computer. I’ve seen it dozens of times. Specifically, check the main engine-to-chassis ground and the smaller ground wires near the thermostat housing. A few minutes with a wire brush and a wrench can save you a lot of diagnostic time and confirm that the PCM is truly the problem.
The Direct-Fit, Programmed Solution
This isn’t just a replacement part; it’s a complete solution. We take a quality, tested Powertrain Control Module and program it specifically for your truck using your Vehicle Identification Number (VIN). This is a critical step that many sellers skip.
Why is VIN programming so important? Your VIN tells us everything about your truck’s original configuration: engine size, transmission type, emissions equipment, and even tire size. By flashing this module with the latest official software from GM, we ensure that it functions exactly as the factory intended. This process corrects old software bugs and optimizes performance and fuel efficiency, often making the truck run better than it has in years.
What You Get:
- โ A reliable Powertrain Control Module compatible with part numbers 16263494, 16265035, and 21811787.
- โ Free VIN programming service before we ship. Just provide your VIN at checkout.
- โ Loaded with the most current GM software updates for improved drivability.
- โ A plug-and-play part that simplifies your repair.
Installation Note
Once installed, you may need to perform a security relearn procedure (often called Passlock or VATS relearn) to sync the new PCM with your truck’s anti-theft system. This is a standard GM procedure and can typically be done in your driveway without special tools. This ensures your vehicle remains secure and starts correctly with the new module.
Guaranteed Compatibility
This module is a direct replacement for a wide range of GM trucks and vans from this era, not just the GMC 3500. It is guaranteed to fit and function in the vehicles listed in the compatibility chart, provided the original part number matches one of the following: 16263494, 16265035, 8162634940, 218-11787, or 21811787. Please verify the part number on your original module to ensure a perfect match.