This is a solution - not just the problem

A while ago the parking sensors on my '09 Estate started to just gave a continuous bleeeeep as soon as Reverse was engaged; then a week or so later, stopped working completely.

Pulled the Control box out of the spare wheel well & found water marking on the printed circuit board (which was knack'd).

After hunting around - there's a number of different control boxes depending on year, number of sensors, and (probably) what they just fancied fitting! Even Jags ordered me the wrong one - from the chassis number!!

Finally got the RIGHT box (£165 !!!) & fitted it: Fronts worked fine, Rears were REALLY quiet???? Spoke to the dealership mechanic who said a 'fried' board will often 'fry' the back sounder too ... GRRR

New sounder from Jags = £18 +VAT ... identical part from a FORD parts man on Ebay = £10 delivered

It's fiddly to fit but easier with a friend/wife looking in through the side window giving Golden Shot style directions ("Left a bit / Right a bit" etc), but the end result is everything working as it should

Here's a link to the Ebay seller & I've attached directions for doing the job:-
Genuine Ford Parking Control Aid Speaker 4501599 | eBay