serviced trans today

serviced the trans on 01 f1 today removed oil after road test,fluid was actually in good shape it had about 5000 miles on it.filled with redline 75/90 ns and added red line fm 4 onzs.road test,shifts great.this forum is great so much info.the only concern so far i have is when you start up while eng is cold slow down light flashes for about 1-2 mins ,no driving concerns,foc changed the right side cat temp 2 months ago,no ck eng light on any ideas,also where is the cat temp sensor located and what does it look like?
thanks