Chrysler Repair: Autotrans downshift to second gear by itself, vacuum line, trans shop

Question
QUESTION: I am not exactly sure of the year but i belive it is the early 90-93 new Yorker with the 3.3l. i am thinking about buying it locally it has a problem of shifting when it should not. from what i know it would shift down into low gear when just cruising at highways speeds. i am assuming it is the vacuum line or the valve, but im not familiar with these cars. i do have 4 older new Yorkers with 3.0s but this one is different and i have not test driving it yet.
ANSWER: Hi Jacob,
That is called going into limp in mode and it is the built-in program that the controller performs to try and prevent further damage to the transmission and allow the car to be driven for analysis/repair. It also will put a fault code in the memory of the controller which can be readout with a Diagnostic Readout Box II at a dealer or trans shop. The repair possibilities can then be assessed based on the fault code. The access plug in called the data link connector and it is under the dash near the steering column. So if you are seriously interested in the car then get a code readout and let me know what you find it to be. The shop that does the reader should tell you the code number, the name of the code, what it means, what they think is the repair, and how much it is estimated to cost.
The rebuild of any automatic trans is expensive, and these are no different.
Roland

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QUESTION: but i thought that was only for upshifts too quick. it upshifts fine apparently but downshifts when just cruising. i can easily get ahold of a junkyard tranny for free so i would likely just change the whole thing out anyways. i am buying it for $100 i figure even if it doesnt work out i can just part it out and make money off of it

Answer
Hi Jacob,
This behavior I describe is an inappropriate downshift when you would not expect it to do that, e.g. cruising with no hills or need to accelerate, etc.
It puts the trans in the gear that requires the least amount of clutches, etc. You will have a challenge finding one of these electronic transaxles in a junkyard that is working fine, as I suspect the failure of the trans is one of the commonest reasons for them being there. The cost of a rebuild approaches $2,000, but if you want to take a chance and can part it out or maybe get lucky that the problem is simple, go for it. If you did get a code readout though you would know if the problem is internal to the mechanical parts or if lucky just having to do with the solenoid box that can be serviced without removing the trans and opening it up. So the readout is the key to sizing-up the car.
Roland