Primary Speed Sensor
WARNING: This page is about a different car, the 2010 Nissan Sentra. However, it is still accessible from the selected car via links, so may be relevant.
The shift pattern is changed in accordance with throttle position and secondary speed (vehicle speed) when an unexpected signal is sent from the primary speed sensor to the TCM. The overdrive-off mode is inhibited, and the transaxle is put in "D".