My check engine light came on and my car stopped shifting so l took it to discount auto to have them hook it up to their computer and see whats wrong with it they said that it is a transmission speed sensor so l replaced it and the light went off and came back on after 200 miles so l returned it and said that it was a defected part the new one had the same issue then l realized that even with the old sensor if you disconnect the light will go off for about 200 miles then the light will come back on and it will start shifting bad what could b e causing this

Most likely a wire harness issue. Remove the battery and battery box . Check plugs between body and transmission. Typical VW issue.

Is the speedometer acting up when this is all happening? If so, the gear that runs the vehicle speed sensor is made of plastic and they crack. If not, it is either a problem with the electrical wiring or the transmission control module.