Transmission issue

[Btech]

Being it flashes fault on the display means there is a code stored in the transmission control module, you should be able to get a code on the gear indicator by starting with the key on, turn it off and back on 2x to get active codes, 4x to get stored codes, and 6x to clear codes.
these codes can give you a good idea of where to start, the 2 digit codes you get this way can be somewhat broad sometimes but its better than nothing.