It's amazing what can be determined when you're standing next to the car and don't have to rely on incomplete information that gets mixed up in translation. However, it appears you still don't have an answer.
Warning lights turning on and various systems and circuits not working is an EXTREMELY common problem caused by a defective ignition switch, hence that's the appropriate answer for the minimal information available.
There is only one transmission computer. It shares information with other computers on the car on a circuit called the "data buss". The data buss is powered by the Body computer. It isn't often one computer fails on a Chrysler product. Very few knowledgeable people can be mislead into believing two or more computers would fail at the same time unless 1) a novice caused voltage spikes by welding on the car without disconnecting the battery, 2) someone intentionally poked and stabbed wires to cause damage to multiple computers, or 3) someone is selling you parts you don't need. There is only one legitimate reason to replace two computers at the same time, and it has nothing to do with the symptoms listed.
"a comunicaton problem with the modules and the transmission" is a generic dumbed-down all-encompassing answer that says nothing useful. What is the part number for a communication problem? What will it take to fix the problem? And how does the Anti-Lock Brake computer turn on the warning light on the dash when there's a transmission problem? The gauges don't work, so you replaced the engine computer? Then you replaced a second computer, the transmission controller, and it still doesn't shift? By now you should have figured out something else is wrong and blindly throwing parts at it is the least effective, most costly way to try to find a fix. What if a basketful of new parts isn't the solution? A single wire can be broken open or grounded causing loss of communication between modules and all the problems listed. But so can partial loss of power to all the computers from a very common problem, the ignition switch.
Given the vague, "keep-your-wallet-open" answer, I'd be running as fast as possible to find a second opinion. Why did you go to a transmission shop? The Brake warning lights are on; why didn't you go to a brake specialist? The gauges are not working. Why would you go to a transmission specialist for an obvious electrical problem?
There could very well be a single computer that is shorting out the data buss. That will cause a multitude of problems, the most significant of which is the engine will not run. There can be over 20 computers on your car, and it is just about unheard of to have a shorted module. The fact that the engine runs PROVES there is communication taking place between modules and the data buss is working. What is very common is for the generic aftermarket hand-held scanners, (computers), to not communicate with the car's computers. Many of those scanners will give a message to the effect of "communication failure". That means failure of the test equipment, not a failure in the car. This is why I only use Chrysler's DRB3 computer.
Given the symptoms provided, nine out of ten times, a new computer will not be the cure, and it certainly won't be multiple computers. You may indeed have that tenth car, but that still doesn't explain the symptoms unrelated to the transmission. The body computers on '96 and newer Caravans have been the cause of more problems than usual, but they still don't cause this many problems at once.
If you examine just the dead speedometer problem, two speed sensors send information to the transmission computer. (If one of them fails, the transmission will stay in second gear. That's all). That information is used, in part, to determine when the transmission should shift. The transmission computer sends information on the data buss to the body computer which interprets it, then sends it to the instrument cluster which is an entire computer module onto itself. A failure anywhere along this path can result in a dead speedometer, but that doesn't explain any of the other symptoms. The body computer won't stop the transmission from shifting, and it won't turn on the air bag or anti-lock brake lights. If the transmission computer fails, it will also stay in second gear, but again, what about all the unrelated symptoms?
You need to have a specialist look at your car. I strongly recommend the dealership. The people there are trained only in your model and often know right where to look to quickly find the problem. The only disadvantage to hopping from shop to shop is they have to wonder how many additional problems the previous shop unintentionally put in the car. Every new computer adds a bunch more variables to the original problem. If that new computer or other part doesn't solve the problem, put the old one back in. Computers especially, since they have had software installed specific to your car, and they learn their "personality" from constantly updating information related to operating characteristics of the drive train and other systems.
It's logical, given limited information, and confusing or lacking details, that 90 percent of the answers here will be wrong. Often, trying to provide a helpful answer is met with frustration when we are expected to know the answers to obscure defects on cars we can't see, hear, or perform tests on. Couple that with owners who don't know how to observe and report clues, and you have an impossible situation. You provided much better observations than a lot of people, but I am certain the problem did not start with multiple computer failures. You deserve a better answer than "a comunicaton problem with the modules and the transmission." That's a symptom, not a solution. If the shop can't provide you with a written estimate for repairs, and tell you exactly what is wrong, they are likely going to throw parts at it until "something sticks" and fixes the problem. Once repaired, disreputable shops will charge you for the parts they tried that didn't solve the problem. The warning clue is the lack of a definite diagnosis which is what you still have.
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Wednesday, January 20th, 2010 AT 1:38 AM