If no output pulse is detected from the input shaft speed (PG-A) sensor for 1 second or more while driving in 3rd or 4th gear at a speed of 30 km/h or more, it is judged to be an open or short circuit. In the input shaft speed sensor and diagnosis code P0715 is output. If diagnosis code P0715 is output four times, the transmission is locked into 3rd gear (D range) or 2nd gear as a fail-safe measure.
Your problem is an input and out put speed sensor wich is also located on top of the trans. These sensors measure the speed of the input and output shafts inside of the trans mission, you probably will not be able to get these sensors aftermarket, dealer item only I think.
Also, do not confuse them with the vehicle speed sensor (VSS) which only deals with the engine RPM and vehicle speed.