I drive a 2000 Audi A4 B5 2.8L Quattro Avant

Noticed an old exhaust hanger dangling from my car the other day, jacked it up to find that it is actually a sensor. It is hanging down right in front of the driver side rear wheel. I am not throwing any codes or fault lights so it obviously isn't broken. But I am curious what it is and what it does.

Picture attached!