I have replaced all 4 O2 sensors and even put the spark plug fouler on the one with issue bank 1 sensor 1. Replaced spark plugs and replaced camshaft sensor however the code p0420 comes back. I thought I cleared it and it didn't come back when I fixed it and cleared it I got back code for camshaft sensor so I replaced it cleared code for camshaft and then code comes back for p0420 stuck don't know what else to do except replace catalytic convertor