Mk5 r32 rear reverse censors not working

[itismebigd]

Hi iv got a golf r32 with factory fitted rear reverse censors and the other day when selecting reverse the audible tone came on as usual but when i get close to an object there are no audible sounding indicators to how near or far i am from the object...can anyone sudjest a fix or a way of finding out the cause without a trip to the dealers for vagcom thanks in advance Dougie