So they just seem to have packed in, i press the switch on the dash and the two red lights light up on the sensors on the front dash (but not at the back) for about 5 secs then makes a beep and they turn off again?
i have this problem on my W221 but my loom was sheared off in a crash and I re-soldered it back. I haven't had a chance to look at it again, but one thing I would check is that all the connections are ok and that the actual sensors are seated correctly, i.e not picking up a signal off the bumper.
