paneuro

Hi , I have a 2008 E61 530D M sport and apart from all the other problems I now have a problem with the rear parking sensors. I looked on u tube and there are a few videos explaining how to isolate the faulty sensor but none of these work. I am getting a solid signal whenever I put the car in reverse and have to switch the parking button of. I notice on the display that the image on the I drive screen that there is 1 segment missing at the rear on the nearside but I can't feel or hear any of the sensors ticking which I am told they do. Is it worth buying a new sensor and pulling the bumper of? Any advice, thanks Paneuro.