backing up sensor

To respond to this question, I have to make a few assumptions: you did mean “off?” The fuse that operates this feature is in the under dash fuse-box labeled F2.26 7.5 amp, which also operates the shifter interlock. I would assume that you would also report that you could not get the shifter out of park since the fuse is shared by both circuits. The “Parking assist” button illuminates when it is turned off on the vehicle. If it is lit, you have a concern elsewhere such as the module: PAM (Parking assist module), sensors or wiring. One of the most common concerns comes from some kind of damage to the rear bumper. Repair shops often neglect to repair it properly. Look under your rear bumper at the wiring for the four back-up sensors, see if it is routed properly and damage free. If visual inspection appears to be normal, I suggest a technician with adequate equipment to monitor this module be visited.