Depends on whether the problem is a faulty sensor or damaged wiring. Do you have a scan tool or app that can see real time data? If so, do you see a signal from the rear speed sensor? If so, the problem is most likely the signal itself, which would tend to indicate replacing the sensor. If *not*, check the wiring harness for any apparent damage, check the fuse, check for circuit continuity. If you find a problem in the wiring, fix it and see if it clears up your problem.
Good Luck!
(EDIT: Obviously I'm typing too slowly this weekend!)
Chris