2000 Audi A4 trunk lid won't shut properly

The sensor is part of the latch system, the only other sensor is for the light, and that is just a push button sensor on the frame of the car under the lid. Yo may want to try cleaning the latch, take some brake clean and a towel and spray it out thoroughly, then let it dry and lightly spray some WD 40 or equivalent in the mechanics. Also check to see if any of the bolts are loose and providing play in the latch.