Reversing sensor woes

[Olde English]

My 2005 XK8 reversing sensors no longer work. I get the 5 sec continuous sound at start up to warn me. Have checked fuse, loose connections, to no avail. Is it sensors or could it be the module? Anyone else had this?

[Olde English]

So, the wife asks me to pick her up after a girlies after work thingy, jump in the car, suffer the whine of the warning tone and orff I jolly well go. Going to West Quay I have to traverse some raised ramps (pedestrian crossings), go to park up, sling the old girl in reverse and oh, the sensors are working again.

24 hours on and still working, now either something is loose, or I have jolted some hidden grime off, I have absolutely no idea, is this the true meaning of "a wonder mechanic?" (definition - wonder how that happened then_