context, today, i was just driving with my check engine light on (which to me i thought it was just the p0456 that i’ve been dealing with for a year now, but don’t have time to chase it down) but i wanted to just double check randomly today so, i stopped at autozone and pulled a new code in addition to the p0456 which was p0420 (pending) i know this code specifically since i dealt with it nearly a year ago when i went catless (obx) headers with spacers to get rid of p0420 and p0430, however like many aftermarket headers for this car, its never perfectly flushed when installed. i don’t smell anything coming from the engine bay BUT i do have a fat exahust leak at the bottom of the headers that connects to the y-pipe. my question is, why does p0420 just comes back up after a year of it off? what are some possible causes if it isn’t o2? would it be a header leak that causes it? and also its just 420 and not the combo of 420/430. i believe when i was checking the data on the scanner today for the o2 sensors, b1s1,b1s2 were between 0.8 at idle…so, i’d assume its not o2 sensors? any advice would help. thank you in advanced.