I would like to commend this forum without which I would not have been able to fix my parking sensor problem. I am posting this to clarify something I did not pick up when reading the posts on parking sensors. I read that there was a tick when the parking sensors were switched on so I organised one of my children to sit in the car switching the parking sensors on and off. I now realise that the parking sensors tick constantly the whole time while they are switched on not just once the moment they are switched on as I had thought. I thought that by posting this I might save someone some money which I just wasted on child labour. My parking sensors have not worked since I got he car, but, knowing that the senors should tick, I was able to find the one which was not ticking. It was the nearside rear one. I swapped it with another one and found it was still the near side rear one not ticking. So I checked the wiring and after fiddling with it, one of the wires was so corroded it came away. I removed the bad bit, soldered it back together, and the parking system now works perfectly - no replacement parts required. I have read in these posts that it seems to be the nearside rear wiring which is prone to failing. I do not have the VAG-COM thing but its sound like I should get one.