Land Rover Repair: Landrover Disco II 1999 Transmission suddenly quit while driving!, transmission control unit, odb ii

Question
Hi Nigel, Hope you can help me...My son is in college, and called me stating that while driving (over the course of 1-2 mins) the Disco RPMs started rising while is kept on slowing down, to a point where he was going no more than 5 mph. He parked his car. I had the dealer service his transmission just 3 weeks ago as I noticed an approx 3 sec delay for "Drive" to engage when switching from Reverse or Park. The service reduced the delay to just about a second! Not bad. And three weeks later, this! Can the transmission on this car go out just like that w/o any idiot light coming on and no warning. Vehicle has 107,000 miles, and the engine got new head gaskets approx 2 mos ago. Would clearing error codes via the ODB II "gadget" be a good way to see if the transmission can come out of the "limp mode"(that's where we think it is stuck). No LR dealers within 2 hrs of his school, so any tricks to narrow the problem would be VERY MUCH appreciated!
Thank a lot!
Babur

Answer
If you have an OBDII reader the first thing to do would be to check for codes and see what they mean if you find any.  You should normally find some codes if there is a transmission failure.  By your description, it does sound like a transmission failure.  However, transmission failure is a pretty rare occurence with this car so it is hard to say.  Other possibilities include failure of the transmission control unit or the external gear position switch.