P0430, P1140, P1145, Exhaust pipe

Question

i have a 2001 Pathfinder with OBD codes P1140, P1145, and P0430. I have also noticed that the tail pipe on the muffler has fallen off.
I have read the P0430 is Catconverter and expensive.
what course of action should be taken to correct these?
I read that P1140/1145 should be corrected first. Could the exhaust pipe cause the 0430 code?
thx