i dont care about the knock sensor cause my 02 sensor might have triggered it.. How ever i check code and got REAR HEated 02 sensor.. WERE IS THAT!!! Is that near the cat

 

yes the 0304 sometimes pops up with the o2 sensor code.

the rear heated o2 is behind the cat, it senses if the cat is functioning properly (to keep emissions down)

check the GD forum i believe budha56 (aka The Man, y-pipe gd) has a GD going on o2 sensors now so you can get one cheap.