Reversing sensors gone haywire. How to check them.

Have a 2012 estate and today reversing sensor gave long continuous beep. Next time on the screen its jumping all over the place mainly middle to right hand side. I assume one or more sensors have failed or perhaps wiring. Whats the easiest way of removing and checking them plus is there a way of finding out which one or more thats causing the problem. They are the type that sit flush in bumper and are colour coded to match. Had a quick look but it doesnt seem that easy to get to them without removing bumper. I dont have vcds etc but is there a way of disabling them until I get it sorted or perhaps do without.

Alasdair