Is Your GM Truck or Van Running Rough?
The Powertrain Control Module, or PCM, is the central command center for your vehicle’s engine and transmission. In late-90s GM vehicles like your 1998 Chevrolet Astro, this component is critical for everything from fuel mixture and ignition timing to transmission shift points and emissions control. When the PCM begins to fail, it can cause a cascade of confusing and frustrating problems that can be difficult to diagnose. Symptoms can range from a simple check engine light to a vehicle that won’t start at all.
The Brain Behind the Brawn
Think of the PCM as the brain of your vehicle’s powertrain. It constantly receives data from sensors all over the engine and transmission—like the crankshaft position sensor, oxygen sensors, and throttle position sensor. It then processes this information in real-time to make precise adjustments, ensuring your engine runs efficiently and smoothly. A faulty module can misinterpret this data, leading to poor performance, increased emissions, and potential damage to other components.
From the Diagnostic Bay
We had a 1999 GMC Yukon in the shop that was driving the owner crazy. It would randomly stall at stoplights, but only when it was hot. There were no consistent trouble codes, just a generic P0300 random misfire code that would pop up occasionally. The owner had already replaced the plugs, wires, cap, and rotor. We checked fuel pressure, and it was perfect. After hours of chasing our tails, we hooked up a scope to the ignition control module signal. We noticed the signal would drop out completely just before the engine stalled. Tracing it back, the driver inside the original PCM was overheating and failing, but not long enough to set a specific fault code. We installed a VIN-programmed replacement PCM like this one, performed a CASE relearn, and the Yukon ran perfectly. It’s a classic example of how a failing computer can mimic a dozen other problems.
Diagnosing a Failing 1998 Astro PCM
Identifying a failing PCM can be tricky, as its symptoms often overlap with other failing parts. However, if you’re experiencing several of the issues below, your PCM is a likely culprit. This module is a direct, pre-programmed solution to get your vehicle back in top form.
Common Symptoms of a Bad PCM
- ✔ Check Engine Light: The light is on, and you may have codes related to PCM internal failure or communication errors (U-codes).
- ✔ Engine Stalling or Misfiring: The engine may stall intermittently, run rough, or misfire, especially as it warms up.
- ✔ No-Start Condition: The engine cranks but refuses to start, often due to a lack of spark or fuel injector pulse.
- ✔ Poor Fuel Economy: A sudden and unexplained drop in MPG can be caused by the PCM failing to properly regulate the air-fuel mixture.
- ✔ Harsh or Erratic Shifting: The PCM also controls the transmission, and a failure can lead to delayed, hard, or incorrect gear shifts.
- ✔ Failed Emissions Test: An inability to pass an emissions test is a strong indicator of a PCM that is not correctly managing the engine’s combustion process.
The Plug-and-Play Solution
Don’t let a bad computer keep you off the road. This is a tested, genuine OEM PCM sourced from a salvaged vehicle, ensuring factory-level quality and durability. The most significant advantage is our professional programming service. Before we ship the unit, we flash it with the latest GM-released software updates and program it specifically to your vehicle’s Vehicle Identification Number (VIN). This critical step ensures that the module communicates correctly with all other systems in your vehicle, making installation as simple as possible. In most cases, you will only need to perform a simple security relearn procedure after installation, which can often be done without special tools.
This module is a direct replacement for multiple part numbers, including 09355699, 16266645, 16250279, 16258815, and 9366810. It fits a wide range of GM trucks and vans from 1998 and 1999, including the Chevrolet Express, GMC Savana, Tahoe, Suburban, and S10/Blazer series. Please verify your original part number and consult the fitment list to ensure compatibility.
Frequently Asked Questions
What information do you need to program this PCM?
After you complete your purchase, you must provide us with your vehicle’s 17-digit VIN (Vehicle Identification Number). This allows us to load the exact software and calibrations for your specific make, model, engine, and options.
Is this a new part?
No, this is a fully tested, used OEM part that was carefully recovered from a salvaged vehicle. This provides the reliability of a genuine GM part at a significant cost saving compared to a new unit from a dealer.
Will I need to do anything after I install it?
In most cases, you will need to perform a security relearn procedure (often called a Passlock or VATS relearn) to sync the new PCM with your vehicle’s anti-theft system. This procedure can typically be done without special tools and instructions are widely available online. A Crankshaft Variation Relearn (CASE relearn) may also be required, which needs a capable scan tool.
How can I be sure this fits my truck?
The best way to ensure compatibility is to match the part number from your original PCM to one of the numbers listed (e.g., 9366810 or 09355699). You can also check the detailed fitment list on this page. Providing your VIN for programming is the final confirmation of a correct match.
What if my original part number is not on your list?
Please contact us with your vehicle’s VIN and the part number from your original computer. We can check our extensive database to see if we have a compatible module for your application.