I was driving on the freeway when the gear dropped from 6 to 0 and there was no power to the wheels. The transmission light came on. I pulled over and turned the car off, restarted it and drove off. This problem has now started to surface again. Either the transmission light comes on or it says F6 instead of D1 and the car does not move, I have to turn it off and then start allover again. I took it to a shop but they could not find any codes. Any suggestions please.