And if the pcm says it is the o2 sensor in bank 2 sensor 1 then you have other problems. The bank 1 sensor 1 is the 02 sensor that is in the rear header. The bank 2 sensor 1 is the o2 that is in the cat. The one in the cat is strictly to monitor the cat to see if it is performing correctly and will not cause any problems if it were to go bad.