the 2nd sensor is for monitoring only
it only confirms the cat is doing its job it can be unplugged and the car would run fine but with the lamp on the dash
the front sensor is what controls the fuel i spent 4days trying to sort it all out lol if its rich then it may be your front sensor up the s**tz
get op com on it and see what the front sensor is reading they only work 1v-0v and normally when up to temp give a reading of 850-950mv at idle
heres a dead front lambda (bank1 sensor 1)
and heres a brand new one fitted in its place