Perhaps this will help ???
If they are the same as on the X type, then if you turn the ignition on and put gear into reverse (without running the engine) then put your ear against each sensor in turn, you should be able to hear them 'clicking'. If one (or more) are not clicking then they are faulty. If none are clicking then it could be the module in the boot.
According to my fuse chart, it is fuse 3 (5amp) which is located in the boot fuse box.
EDIT: The fuse also controls other circuits such as bulb monitoring module, s/c fuel pump relay so if these are still working it won't be the fuse.