QuestionI have a 1993 Chrysler T&C van that while driving anywheres from 30-50 mph will just drop into 1st gear or neutral without warning. Once you pull over shut off the van and restart it, it will run normally for a while and then do it again. We had the transmission changed approx 40,000 miles ago and just had it checked today and they said our transmission is fine, but could not duplicate the problem and since the computer said it was fine sent us on our way. My husband has also changed the fluid and gaskets on the transmission. Any ideas?
AnswerHi Patricia,
I believe that the computer readout was not performed with the proper test tool, and maybe not even the proper plug-in site for the test tool. In the first half of the 90's the memory of the transmission controller was read by means of a blue six-pin plug (three pins on a side, rectangular) located below the lower left side of the instrument panel and that plug is different in shape from the one located in the engine compartment that reads only the engine controller (black, 4 pins in a square, 2 pins to the side). The reader must have a cartridge that is capable of communication with the transmission control memory (such as the Chrysler DRB II). I say this because the transmission is downshifting to 2nd gear into what is called "limp-in mode" and a code is always put into the memory of the transmission controller when this happens.
You didn't say if the readout was done at a Chrysler dealer or with a DRB II box, so that is where I stand as to the existence of a clue as to what is wrong by means of getting a fault code. Here is an earlier response I gave to an owner of a '94 with the same sort of history:
"That exact lock up is what happens when the transmission computer notices something is wrong and so it protects the transmission by driving in 2nd gear until it can be serviced so as to protect against any further damage. It is called "limp-in mode".
The chances are there is some internal mechanical wear/damage to the internal clutches of the transmission, but because the cost of rebuilding is so high it is worth spending a little on analyzing whether that is true or not. It may also be the case that the problem is with electrical connections/computer or with the transmission fluid system (hydraulic) and those can be repaired without removing or rebuilding the transmission at much less cost.
The transmission has an electronic controller that has the ability to recognize malfunctions and store them in its memory as two-digit fault codes. You need a readout of the transmission computer which is an electronic test for the presence of coded numbers representing different faults that the transmission is experiencing at the time when it locks up into 2nd gear. An electronic readout device is plugged into a port under the dash to access the memory and tell you the fault code numbers. It would be worth spending about $50 to have this done just in case the problem had to do with the hydraulic or electronic parts rather than the internal mechanical parts because those could be repaired without taking the trans out of the car and dismantling it. So a dealer or a competent independent transmission shop (but NOT a franchise type like Aamco where the usual answer will be to do a "rebuild") with a reader for Chrysler transmissions should be able to do that. Ask for the code number(s), what they mean, what repair is needed and how much it will cost. Be sure that they have the 6-pin ("bus diagnostic connector") reader plug adapter that will give them access to the memory via the port under the dash. This is NOT the same plug as is in the engine compartment (which is also a 6-pin plug but arranged differently) for accessing the engine controller memory. Their reader also has to be equipped with a program (cartridge) that accesses the transmission computer. A Chrysler dealer will have this device called a DRB II, but will charge more for the readout. You might get an agreement to credit the cost of the readout to a repair, if you agree to let them do it.
Then write back and we'll evaluate what you were told, particularly what are the fault code numbers. I have the '94 factory repair manual and can look up what the numbers mean and what needs to be done to fix this."
Also check the warranty provisions of your rebuild to see if the shop that performed that might be liable for the repair.
Please let me know if you get a proper readout and fault code numbers and we can compare notes with the manuals.
Roland
PS: Which type of trans fluid did your husband use in his change out? Did he get all 10 quarts out, or just drain the pan which only changes out less than half of the total fluid in the unit (rest is in the torque converter and radiator core/lines)?
