I have writen before about this problem. The car will all of a sudden go into 2nd or 3rd and stay there. the "service Engine" light will come on. If I stop and turn off engine and let things cool down it might drive ok for a while then, but service light stays on. the car will not shift gears, but stays in same gear all the time. the dealer has tried several things, speed sensor, solenoids for changing gears, wiring harness. I just drove it for several months on no long trips, and was ok until yesterday. I could really use some help on this. Also, the neutral light flashes during this time, the drive light is still on.
Thanks

 

you need to pull the transmission codes (NOT the engine codes... they're not accurate) to start the diagnostic procedure.