P0720 Nissan -

Question

I am intermittently getting this error code, which immediately puts the engine in "limp mode"
making it impossible to proceed and requires assistance from the RAC.
When the car is carried to the nearest Nissan dealer this code shows up on their diagnostic equipment as a "Past error", so no remedial work is carried out, they reset the dashboard light and the car runs fine until the next time it happens.

Answer 1

what year is the car?

are you under powertrain warranty? if so it should be covered

P0720 is for the speed sensor 

there are two sensor primary and secondary 

Primary picture below

Secondary speed sensor