The sensor has two tines that project into the rear section of the topmost lefthand rack channel. The tines are spring loaded so that when the racks are removed the tines are forced into the channel which closes a circuit that allows the cleaning cycle to run. When the racks are installed the tines are pushed out of the channel which opens the circuit and prevents the clean cycle from running. The spring in the Rack Sensor weakens with time so that the tines don't fully extend when the racks are removed preventing the CLEAN cycle from running. Using a small curved medical forceps (available in most hardware stores, $6.99 on Amazon) the tines can be pulled forward after the racks are removed closing the Rack Sensor circuit so that the clean cycle can run.
