Daughter took her car for an oil change and courtesy check. They found 3 codes one which I cleared P0328 by replacing and relocating the knock sensor the other 2 I read is either a catalyst converter for bank 1 and 2 or CO2 sensors. This vehicle has 4 CATs, pre and post so I assume the codes are picked up from the pre cat which also has CO2 sensors before and after. Would this be a correct assumption? I was looking at the Walker brand CATs which I understand fit in with no issues.