I have this problem with my PDC system where only the center two sensors work on the rear bumper. So the 4 sensors on the front plus the two corner sensors on the rear don't work as in there is no ticking sound and DIS can't read any data from them.
What I've done so far is replace one rear corner sensor to see if the sensor was broken. This did not help as the replaced sensor also would not 'tick'. After this I also replaced the PDC controller, only to find out the replaced module acted exactly the same.
What else could I do to tackle this issue?