So I have this fault code that has been coming back over the last 200 miles or so. - Cars running perfectly. Checked all lines for leaks, not smoke tested though. Checked wiring on both sensors and seems ok (no damage). Pre cat was changed for a new genuine sensor about 2.5 years ago. I’m stumped, would it be worth changing one if not both of them? Or is my cat knackered? Thanks in advance George.