Output Speed Sensor fault – Nissan Sentra 1.8L 2005

I have a Sentra that is occasionally refusing to shift into second gear. It has once or twice even started out in second gear and refused to shift into another gear. This is all remedied by a shift into neutral, while driving, and cycling the engine off and then starting it again. Shift back into drive, and it resumes normal operation, usually for the duration of the drive.

I recently drained and filled the transmission with correct OEM-spec transmission fluid and it helped a little bit. However, did not fix the problem. The code it is throwing is a P0720.

I checked the wiring to the sensor, and found no breaks or obvious indicators of excessive wear. I ohmed out the cable from the connector nearest the transmission to the actual sensor connector and got no resistance, which indicates a good connection, at least while stopped.

Upon reviewing the freeze-frame from the diagnostic computer onboard, I’ve noticed that this problem typically throws a code at ~40mph every time. Regardless of the throttle position or the engine load, this problem occurs almost exclusively at 40mph. I am not driving 40mph in first gear, obviously.

1. Why would this output speed sensor code come up at 40mph?

2. Is this a standard indicator of a sensor needing to be replaced?

3. How often do speed sensors need to be replaced?

4. Is there anything else I need to know about this problem, as you see it?

Brand: Nissan
Model: Sentra
Year: 2005
Engine: 1.8L