Originally Posted by bambbrose

just becuase it has both o2 sensors hooked up doesn't mean that the secondary sensor is getting the correct reading... the secondary sensor knows that its after the cat and expects a cleaner air flowing through it.. if the cat is gone it will read out of spec and will throw the code.. you need to get either, a) an o2 simulator, or b) a stock ex cat or aftermarket cat with o2 bung after it and hook your second sensor after the cat. then you'll be good

edit:
also that code: "P0140 o2 sensor circuit no activity detected bank number 1 sensor number 2"

the second sensor isn't hooked up... that or it's so jacked that it isn't even sending a signal