PCM replacement

All in an attempt to prevent car theft, but going back to GM's anti-theft systems in the '90s, they were real effective, at keeping owners out of their cars.

Here's one more tidbit I want to add. I don't think this applies to your Jeep, so it's mainly for the benefit of owners of other models who may be researching this topic. I've witnessed this three times, and been involved with two of them. The first was on a '92 Dynasty at the dealership. This is where I first learned of this. The second was that friend of mine has a body shop where he specializes in rebuilding smashed one and two-year-old Chrysler products, mainly trucks, and the third was on a '95 Intrepid used by one of Chrysler's trainers, then donated to my community college.

Let me start with my friend who rebuilt an early 2000s Neon. One of the last damaged items to be replaced was the Engine Computer. To verify everything else was okay, he borrowed the computer from another friend's car. The rebuilt car fired right up and ran fine, so all that was needed was to order his own computer. As soon as they put that borrowed computer back into his friend's car, it was a crank / no-start. They trailered it to a dealership, and the fix was to replace the Engine Computer and the Body Computer at the same time.

In the cases of the Dynasty and the Intrepid, both also needed replacement Engine and Body Computers at the same time. The owner of the Dynasty replaced the Engine Computer himself earlier, which turned out to not be the cause of the original problem. One of my students borrowed the Engine Computer out of our Intrepid to see if it would solve a problem in his car. It did not, but now our Intrepid was also a crank / no-start once the original computer was reinstalled.

What happens is the car could have factory anti-theft from the factory, or it could not have that option. If it does, the software in the Engine Computer and in the Body Computer has the programming for that. Anti-theft programming can not be undone except by the people who rebuild those computers. A better way to say it is that programming is in both computers, but it was never activated if the car didn't come with the optional anti-theft system

When you have a car without the anti-theft system, you must only install replacement Engine or Body Computers that also have never had it activated. As long as that remains true, you can swap computers back and forth all day and never cause a problem. Also, when you buy a replacement computer from the dealer's parts department, they always come with anti-theft not activated.

This is where the potential problem comes in. If your car has the factory-installed anti-theft system, lets say you replace the Engine Computer with a new one from the dealer, the Body Computer will teach that anti-theft programming to the new computer the instant you turn on the ignition switch. You don't have to do anything special, and there's no indication that change has taken place. Both computers will function normally. The same is true if you replace the Body Computer. It learns the anti-theft programming from the Engine Computer. In either case, once that programming has been activated, it can't be deactivated. It's burned into the software permanently.

It's when you take a used computer with anti-theft system activated, and put it in a car without the factory-installed system, it teaches it to the other computer the instant you turn on the ignition switch. Now both computers need to see the "disarm" signal from the door lock cylinder or remote key fob, before they will work, but those don't exist, so that signal is never coming.

At this point competent do-it-yourselfers assume the replacement Engine Computer is defective, so they try another one. That one also learns the anti-theft programming if it wasn't already activated. This will go on and on until it is realized both computers have to have deactivated software, and be installed at the same time. It took me most of the school year to convince my tool room attendant of this. He kept on replacing computers one at a time, and never got that engine running until I found a pair of computers without the anti-theft activated, and had a student install both at the same time.

One important variation of this is on '97 Caravans, and probably other model years. In these vans, one computer doesn't teach the anti-theft programming to the other one simply when turning on the ignition switch. Instead, that occurs when the lift gate is unlocked with the key. There's a switch in the latch assembly that triggers that learning. That switch doesn't exist on vans without the anti-theft system, so a replacement computer will never teach it to the other computer. The new computer with activated anti-theft will not work, as before, but it won't harm the other computer. In this model, it is safe to just try multiple computers until you stumble across one with the anti-theft not activated. That one will work like normal.

I have updated the first response to give you the PCM replacement instructions. Please check it out.

Thanks, Ken.

You'll find the torque specs in the fifth panel. Also note there's no mention of the SKIM key. You only have to enter the vehicle ID number with the scanner. You don't have to rewrite the mileage for the computer to work, but it's important to do so for two reasons. The first is many vehicles in this time period had truck emissions systems that included a "Maintenance Required" light on the dash. Those turned on based mostly on mileage, with a little variation from driving conditions. That was to inform owners it was time to have emissions system components inspected. For example, on older Dakotas and Caravans, that light turned on at 60,000 and 120,000 miles, then never again. If you stick in a replacement computer with lower mileage, the light could turn on again shortly after that service was already performed.

The second reason is the Chrysler trainers told us there is data stored in the computer that we can't see or change, but if law enforcement officials send it back to Chrysler, they can see if emissions-related recalls were performed, which diagnostic fault codes were set in the past, when they occurred, and how long it took before the defect was solved. That's all based on mileage, so they want it to be right.

Given how much more advanced aftermarket scanners are today, I would expect almost any independent repair shop could enter this information, but you'd have to get the vehicle there.

That doesn't sound possible, but please keep me updated. I have a suspicion they're going to enter the VIN for you, then send it back.

I never heard of that. The only thing I found is the need to program the VIN into the replacement computer. That is done just before the computer is shipped to you, so you just plug it in and you're done.

Honda is way different than Chrysler. There's a large group of trainers that develop classes for the mechanics from independent shops so they can get the same training as those from dealerships. In my area, we have a fellow who owns a shop in Jolliet, IL that specializes in the one out of a hundred cars no one else can figure out. Their main customers are other shops. These instructors also collaborate with corporate trainers from the manufacturers.

The consensus among these instructors is when it comes to "customer-friendly" business practices, the world's leaders are Hyundai, Toyota, and Chrysler, in that order. Chrysler has by far the longest list of innovations that benefit car owners going back to the '50s. Those include the first "AC generator for 1960, (they copyrighted the term, "alternator"), first electronic voltage regulator, first electronic ignition, computer-controlled ignition, lock-up torque converter, first anti-lock brakes, (1969), air bags, and computer-controlled transmission. All other manufacturers always come out with their own versions a few years later.

GM, BMW, VW, and Audi are on the bottom of that list. GM in particular has a whole bunch of policies that benefit GM, at the expense of their customers, and one of those is you can no longer grab a computer from a salvage yard or any other car and just pop it into yours. You must have the VIN programmed in, and they won't allow any shop other than the dealers' to do that. Most of them will only program a new or rebuilt computer that they sell you. Unfortunately, other manufacturers copied that too, but every time a manufacturer puts a road block in our way, the aftermarket industry comes up with a solution. The latest one I've heard about is Matco has a programmer that works much like a scanner, but without all those functions and features. It only allows you to enter what is necessary to make a computer work in your car. I don't know how long these have been out, but it might pay to ask as some local shops.