If your workhorse 1999-2000 Chevrolet 3500 Pickup is suddenly running rough, refusing to start, or throwing a stubborn check engine light, the problem often points directly to a failing Powertrain Control Module (PCM). As the central computer for your engine and transmission, a faulty PCM can cause a cascade of frustrating and hard-to-diagnose issues. I’ve spent two decades under the hood of these trucks, and I can tell you that chasing intermittent electrical gremlins is no one’s idea of a good time. This isn’t just a replacement part; it’s a reliable, long-term solution to restore your truck’s performance and dependability.
We take the guesswork and hassle out of the repair. This PCM, part number 21811787, arrives at your door pre-programmed with the latest official GM software updates, specifically matched to your truck’s Vehicle Identification Number (VIN). This means no expensive trips to the dealership for programming. It’s designed to be a direct-fit, plug-and-play solution that gets you back on the road or to the job site with confidence.
Is Your GM Truck Showing These Symptoms?
A failing PCM can manifest in various ways. Over the years in my shop, I’ve seen these modules cause some truly baffling problems. If you’re experiencing any of the following, a faulty PCM is a very likely culprit:
- âś” Unexplained Check Engine Light (CEL) illumination
- âś” Stalling, sputtering, or rough idling
- âś” Harsh or erratic automatic transmission shifting
- âś” A complete no-start condition where the engine cranks but won’t fire
- âś” Noticeable decrease in fuel economy
- âś” Failure to pass an emissions or smog test
- âś” Diagnostic Trouble Codes (DTCs) stored in memory, especially communication codes like U0100 or internal processor failure codes like P0601, P0602, or P0606.
From the Diagnostic Bay: The Ghost in the Machine
I remember a customer bringing in his ’99 Silverado 2500 with an issue that had three other shops stumped. It would run perfectly for days, then suddenly start shifting hard and lose power for an hour before returning to normal. There were no consistent codes, just a history of random communication faults. We checked wiring, grounds, and sensors for a week. On a hunch, we swapped in a known-good, programmed PCM. The ‘ghost’ was gone. The original module had an internal hairline crack on the board that would separate when it got hot, cutting communication just long enough to cause problems but not long enough to set a hard fault. This is a classic failure mode for these units.
A Straightforward Guide to Installation
Replacing the PCM on these GM trucks is a manageable job for a DIYer with basic hand tools. Our pre-programming service handles the most difficult part, but you’ll still need to perform a security relearn procedure after installation, which is simple and requires no special equipment. Here’s a general guide:
- Safety First: Disconnect the negative terminal from your truck’s battery to prevent any electrical shorts.
- Locate the PCM: On most 1999-2000 Chevy 3500 pickups, the PCM is located in the engine compartment on the driver’s side, near the fender or firewall.
- Disconnect the Connectors: Carefully unclip and remove the large wiring harness connectors from the old module. These have locking tabs, so be gentle to avoid breaking them.
- Remove the Old Module: Unbolt the PCM from its mounting bracket. It’s typically held in by a few small bolts.
- Install the New PCM: Mount your new, pre-programmed PCM into the bracket and securely re-attach the wiring harness connectors. You should hear a ‘click’ as they lock into place.
- Reconnect the Battery: Re-attach the negative battery terminal.
- Perform Security Relearn (CRITICAL): You must perform the GM security relearn procedure (often called a CASE relearn) to sync the new PCM with your vehicle’s anti-theft system. This typically involves a sequence of turning the key to ‘ON’ for 10-15 minutes, then ‘OFF’, repeated three times. Your truck will not start until this is completed.
Why Choose a VIN-Programmed Module?
Getting a 1999-2000 Chevy 3500 PCM from us eliminates the biggest hurdle in this repair. A blank module from a parts store or salvage yard won’t work; it must be programmed. Dealerships can charge hundreds for this service alone. We use your VIN to load the exact calibration file your truck needs, including all factory-issued drivability and emissions improvements. This ensures your engine, transmission, anti-lock brakes, and other systems all communicate correctly, restoring original performance and reliability.
Verified Vehicle Compatibility
This module is a direct replacement for part numbers 16263494, 16265035, 8162634940, and 21811787. Please verify your part number or use the compatibility list below. After purchase, we will require your vehicle’s VIN to ensure a perfect software match.
CHEVROLET 2500 PICKUP 00 Electronic Control Module; gasoline (LH front engine compartment)
EXPRESS 1500 VAN 00 Electronic Control Module; (LH rear engine compartment)
EXPRESS 2500 VAN 00 Electronic Control Module; (LH rear engine compartment), gasoline
EXPRESS 3500 VAN 00 Electronic Control Module; (LH rear engine compartment), gasoline
SAVANA 1500 VAN 01-02 Electronic Control Module; (LH rear engine compartment), ID 16263494
ASTRO 00-01 Electronic Control Module; (LH front by battery), ID 16263494
GMC 3500 PICKUP 00 Electronic Control Module; gasoline (LH front engine compartment)
EXPRESS 2500 VAN 01-02 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
S10/S15/SONOMA 99-00 Electronic Control Module; (RH front engine compartment), 4.3L
SAVANA 1500 VAN 00 Electronic Control Module; (LH rear engine compartment)
ASTRO 99 Electronic Control Module; (LH front by battery), (4.3L), ID 16263494
ISUZU HOMBRE 99-00 Electronic Control Module; (RH front engine compartment), 4.3L (6 cylinder)
SAFARI (GMC) 99-01 Electronic Control Module; (LH front by battery), ID 16263494
SAVANA 3500 VAN 01-02 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
EXPRESS 1500 VAN 99 Electronic Control Module; (LH rear engine compartment), ID 16263494
GMC 1500 PICKUP 99 Electronic Control Module; 5.0L, (LH engine compartment), ID 16263494
BLAZER S10/JIMMY S15 98 Electronic Control Module; (RH front engine compartment), w/build date opt ZN4
GMC 1500 PICKUP 99 Electronic Control Module; 5.7L, (LH engine compartment), ID 16263494
SAVANA 3500 VAN 99 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
SAVANA 3500 VAN 00 Electronic Control Module; (LH rear engine compartment), gasoline
TAHOE 00 Electronic Control Module; Classic style (LH front engine compartment)
YUKON 99 Electronic Control Module; (LH engine compartment), ID 16263494
ESCALADE 99 Electronic Control Module; (LH front engine compartment), ID 16263494
ESCALADE 00 Electronic Control Module; (LH front under battery)
EXPRESS 2500 VAN 99 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
S10/S15/SONOMA 98 Electronic Control Module; 6-262 (4.3L), w/build date opt ZN4
YUKON 00 Electronic Control Module; (LH front under battery), Denali
BRAVADA 98 Electronic Control Module; (6-262, 4.3L), w/build date opt ZN4
CHEVROLET 3500 PICKUP 00 Electronic Control Module; gasoline (LH front engine compartment)
ENVOY 99-00 Electronic Control Module; (RH front engine compartment)
EXPRESS 1500 VAN 01-02 Electronic Control Module; (LH rear engine compartment), ID 16263494
EXPRESS 3500 VAN 99 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
GMC 3500 PICKUP 99 Electronic Control Module; gasoline (LH front engine compartment), ID 16263494
ISUZU HOMBRE 98 Electronic Control Module; 4.3L (6 cylinder), w/extended build date opt ZN4
SIERRA 1500 PICKUP 99-00 Electronic Control Module; (LH front under battery), 6 cylinder
SAVANA 2500 VAN 00 Electronic Control Module; (LH rear engine compartment), gasoline
SUBURBAN 1500 99 Electronic Control Module; gasoline (LH front engine compartment), ID 16263494
CHEVROLET 1500 PICKUP 99 Electronic Control Module; 5.7L, (LH engine compartment), ID 16263494
EXPRESS 3500 VAN 01-02 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
GMC 2500 PICKUP 00 Electronic Control Module; gasoline (LH front engine compartment)
SILVERADO 1500 PICKUP 99-00 Electronic Control Module; (LH front under battery), 6 cylinder
SUBURBAN 2500 99 Electronic Control Module; gasoline (LH front engine compartment), ID 16263494
BLAZER S10/JIMMY S15 99-00 Electronic Control Module; (RH front engine compartment)
CHEVROLET 3500 PICKUP 99 Electronic Control Module; gasoline (LH front engine compartment), ID 16263494
SAVANA 1500 VAN 99 Electronic Control Module; (LH rear engine compartment), ID 16263494
TAHOE 99 Electronic Control Module; gasoline (LH front engine compartment), ID 16263494
BRAVADA 99-00 Electronic Control Module; (RH front engine compartment)
CHEVROLET 1500 PICKUP 99 Electronic Control Module; 5.0L, (LH engine compartment), ID 16263494
SAVANA 2500 VAN 99 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
SAVANA 2500 VAN 01-02 Electronic Control Module; (LH rear engine compartment), gasoline, ID 16263494
ENVOY 98 Electronic Control Module; (RH front engine compartment), w/build date opt ZN4
GMC 2500 PICKUP 99 Electronic Control Module; gasoline (LH front engine compartment), ID 16263494
Frequently Asked Questions
Frequently Asked Questions
How do I provide my VIN for programming?
After you complete your purchase, you will receive an email with instructions on where to send your VIN. You can also add it to the ‘notes’ section during checkout. We cannot ship your part until we receive the VIN.
Is this part difficult to install myself?
For someone with basic mechanical skills, this is a very manageable installation. The most important step is performing the security relearn procedure after the physical installation. No special programming tools are needed.
What if my part number isn’t listed?
The listed part numbers (16263494, 16265035, etc.) are the most common, but this module fits a wide range of vehicles. As long as your vehicle is on the compatibility list, we can program this module for you. Providing your VIN is the best way to guarantee a match.
Will this fix my transmission shifting problems?
In many cases, yes. The PCM controls transmission line pressure and shift points. A failing module is a very common cause of erratic shifting, slipping, or delayed engagement on these GM vehicles. This programmed module restores the correct shift strategy.
Does this come with the latest software?
Yes. We program every module with the most current GM-released calibration available for your specific VIN. This helps resolve many common drivability issues that were addressed by GM after the vehicle was built.