Ok this is a thanks to everyone who could reply to me after my rear end affair with a girl earlier this week that resulted in my pdc going wrong (flashing light on the pdc button and one long beep). Firstly I diagnosed which one was off, it wasn't making the clicking noise as I put my ear against it when the parking sensor button was on and key in postion 2.
After popping the tow point cover nearest to the 'bad' pdc sensor I could see just behind the affected sensor and that the cables were cut (due to collision ealier in week)....Soooooo remove bumper under the watchful and in patient eyes of the father in law, first time I tried it. Here are points for anyone going forward in the future:
1.Very good idea to have someone to assist
2. watch this video
https://www.youtube.com/watch?v=QkPxUSSa0L8
or if by the time you read this post link is dead then do a search for E53 X5 Bumper Removal (note this is for the facelifts) 2min vid with some scenes speeded up but it is great
3. Please see attached pic and be very careful with the disengaging of clips 4 from the slots as show in item 5, something that is not mentioned in vid...I got a bit clumsy and broke item 4 on one side, but somehow bumber is still back on ok looking, and believe it was ready to go after a botched removal replacement job when I left it at a garage for a bumper respray.
As for pdc sensor I ordered a new one but the 3 cables leading to the connector that attached to sensor were cut, soldered em together again, was tight as they were cut very close to the end of the connector plug, taped em up even put some heatshrink on em did the testing of the sesnors, and then put it all back together.....Loooong afternoons work, with the father in law now being owed a favour, so looks like more boring hours of oilve picking to placate him...hmmmmm