DTC P2765: Input Speed Sensor: Description
WARNING: This page is about a different car, the 2011 Nissan 370Z. However, it is still accessible from the selected car via links, so may be relevant.
Input speed sensor is installed in transmission and detects transmission input shaft speed. ECM receives input speed signal and performs SynchroRev Match mode (S-MODE) control according to input speed signal.
Courtesy of NISSAN MOTOR CO., U.S.A.