Park Aid inop

Does anyone know how to diagnose/repair the parking aid option? Mine quit suddenly. One red light flashes whenever I put it in reverse.

the over head park aid switch is it in the on pos? there may be a broken wire going to the sensors in the bumper. you could have a look and see. if the van has seen gravel road use this may have broke a wire to the sensors. keep us posted. 463

The overhead switch is on. With it off, none of the lights do anything. I removed the bumper cover, checked continuity of the entire harness and cleaned all the sensors. Still nothing but one flashing red light indicating the system has a problem. I will check fuses and CBs, but think they must be OK or the switch and the one light wouldn't work. ANy other ideas? There was an earlier thread where somebody emailed a couple memebers some kind of trouble-shooting procedure, but I lost track of who it was.