Just learned yesterday via FAA email that my ADSB install done in Aug 2018 has had Mode C and Baro Alt problems since new. After installation my system was test flown and adjusted by phone app until I received a good PAPR with no flags. I have assumed that my system has been operating faultlessly over the last year, not true. I'm corresponding with uAvionix and the avionics shop that did the work. I have spoken with an FAA ADSB team rep, he was informative and helpful. I learned that of the 100,000 ADSB systems installed about 7,000 are faulty. The FAA will "filter" me out of the ADSB system in 45 days unless I correct my ADSB faults.