UKPassats

I got 2004 1.9 TDI 5-speed automatic gearbox 96 kW Passat. Lately when starting my car, the gearbox goes to limp/safe mode and it's stuck in 3rd gear. Sometimes shutting off ignition and restarting car helps but not lately. I ran VAG diagnostics and it showed N215 and N217 solenoid. I took my car to repair and they deleted these codes and then different codes came and car went to safe mode again. They said it's not mechanical problem. I got same problem last year and then wires going to transmission control unit were cleaned and soldered. I checked these wires and they seemed to be ok. I checked the wiring diagram and wires from transmission control unit goes to 16-pin connector located in ?valve body? Does anybody know if this connector can be reached somehow inside the car? In manual it requires that it's removed under the car.