The reverse warning system on my 850 went belly up for good last week. Instead of the single beep I used to get when I put it into reverse, telling me the system was operating, I now get a steady beep lasting six or so seconds and then quitting. After that you can back into a concrete wall without it uttering a single sound. I have cleaned the sensor surfaces, even lightly sanded them, thinking that the paint shop had applied too much paint when I had the bumpers repainted. But I still get the long beep and no warning when I back toward anything.

Have one or more sensors gone kaput, or the little motherboard control box itself? Have searched the net and 850 manuals and there is nothing out there about trouble shooting this item. I don't know if even Volvo has a brochure out on it. The installation instructions that came with it contain no information about probable causes if it fails. Any help greatly appreciated.