I am posting for my hubby who is still stranded with our girls waiting on the tow truck We have a 96 Town & Country LXI 3.8 and the tranmission died today (not fun with a baby and 4 y.o. in the car!) and it has been towed back to our driveway. This is our second, but very necessary vehicle - my husband recently got laid off so this is like the worst time for something like this to happen as he has interviews out of town lined out. Anyways, he has run the OBD II scanner and it says:

720 – speed sensor
731 – incorrect gear ratio # 1

Right now, it wont even shift into neutral or anything else. Anyone have any ideas? I have looked on the net but cant find anything conclusive to try. He was an auto mechanic many years ago but not a transmission expert but due to our current situation he is willing to give anything a go since the alternative is it sitting in our driveway and having no transportation.

Thanks in advance for any advice. We are calling around for used/junk transmissions but so far cheapest price we got is 600 and we just dont have it.

 

I have not worked on the auto transmissions of these cars but have on numerous other electronically controlled transmissions from other manufacturers. I don't know what is wrong with it but sometimes it is worth checking the simple things first.

Based on the first error - 720 speed sensor

Tell you husband to try and check the sanity of all the electrical connections not only to the transmissions but also at the differential he should find the vehicle speed sensor. It would be worthwhile just taking the plugs off making sure they are dry inside, that there are no broken wires and that they are making a good connection.

Also it is worth looking at the actual cables from the shift lever to the transmission and make sure they are working properley.

Under the hood above the right hand fender is the transmission control module. Also check all wires/plugs attaching to this.

Lastly check the oil in the box, it must be at the correct level AND MUST BE a nice red colour. If it is brown or black and smells burnt you have serious issues. If the colour is dark an oil flush and change may help.

A bit more info on how the box was behaving before it failed may help others to try and diagnose other possible faults. i.e. Was there any slipping or grabbing, had your husband done anything to it before hand e.g. add oil etc etc.

 

Checking all the connectors is a good idea. The transmission computer uses a number of sensors to operate the transmission, so this stuff is important. Two very important sensors on the tranny are the input speed sensor and the output speed sensor. The computer uses these to tell that the transmission has shifted properly. The computer can match the ratio between these sensor readings with the ratio for the expected gear and tell if the transmission shifted properly. When something is wrong, the computer shuts off automatic control and the transmission defaults to "limp-in mode" in which the car should operate only in 2nd gear and reverse.

It's not uncommon for one of the speed sensors to fail causing the tranny to enter limp in mode. The sensor's aren't that expensive and are pretty easy to replace-- they're threaded into the front of the tranny-- so people in your circumstance will often replace them to see if it helps.

I think you said that the van won't drive at all though-- that means it's not even working in "limp-in mode". Since limp-in mode is entirely mechanical (it makes no use of the sensors or transmission computer), not even having limp-in mode strongly suggests an internal mechanical failure rather than an electronic one.

As mentioned above, make sure the fluid level is good and fluid is in good condition before condemning the tranny based on this though-- extremely low fluid could cause this problem too.


Edit: I should add that your husband can get access to all of the factory service information pretty cheaply through a service like alldatadiy.com. It's only about $26 and gives you the factory service manual, wiring diagrams, diagnostic flow charts, etc. If this is an internal mechanical problem then the solution is painful, but obvious-- you'll need a used/rebuilt tranny. If it seems to be an electrical problem, your husband (as a former mechanic) may be able to use the service information from a site like that to do some real diagnosis instead of just throwing parts at it.