I have an 09 quattro S-line convertible. My TPMS light came on so I added air to all tires to bring them back up to 36 PSI. The light didn't go off. Why?

 

How long did you wait? Can the light be reset with a tool? Are you sure TPMS devices are all OK, i.e. no recent tire work? Knowing nothing about Audi I think you may either need to ride around for 50 miles or so or have the light reset.