DTC P1723 CVT Speed Sensor Function: Description

WARNING: This page is about a different car, the 2008 Nissan Maxima. However, it is still accessible from the selected car via links, so may be relevant.

The input speed sensor (primary speed sensor) is included in the control valve assembly.
The vehicle speed sensor CVT [output speed sensor (secondary speed sensor)] detects the revolution of the parking gear and generates a pulse signal. The pulse signal is sent to the TCM, which converts it into vehicle speed.
The input speed sensor (primary speed sensor) detects the primary pulley revolution speed and sends a signal to the TCM.