There shouldnt be any additional sensors. These would be passive. Otherwise folks would get a cel from just an exhaust
No sensors but there is a secondary cat inside the factory muffler, I just checked my stock 17 V10+ muffler
2017 mexico blue R8 V10 plus -10.64 @ 132mph stock / 10.56 @ 130.6mph with quicksilver exhaust
2015 red GTR BE - 10.03 @ 136mph with FBO E85 SOLD
Definitely not normal...in the for sale section.