Diagnostic code P0705 OBD2 refers to the switch, whether internal or external, which is located in the transmission. Its function is to give a signal, either to the Power Train Control Module (PCM) or to the Transmission Control Module (TCM), indicating the position of gear changes, such as positions N, D, P, and R. It should be mentioned that the backup lights can also be controlled by the Transmission Range Sensor (TRS), in case it is external.
Basically this code implies that there is a fault in the Transmission Range Sensor (TCM), as it may be sending a wrong or incorrect signal or even not send any signal to the computer that identifies the position of the gear.
The PCM and the TCM receive signals from the Sensor VSS (Vehicle Speed Sensor) and from the TRS Sensor (Transmission Range Sensor), when the vehicle is in motion. If for example; The signal from the TRS sensor indicates that the vehicle is parked, but the signal from the VSS sensor indicates that the vehicle is moving, the DTC code P0705 is established. It should be noted that the fact that the Transmission Range Sensor (TRS) when external is faulty is common, since it is exposed to the weather and other elements that may affect it.