I own a 2004 Honda Civic EX coupe. I got a P0420 code on the car and wanting to know if it’s my Cat or 1 of the 02 sensors the upstream or the downstream. I tried the cleaning the cat system but still get the code I have checked the sensor good connections and today I replaced the fuse to for the LAF heater due to the other looked bad but still good. Any thoughts of what to do next? Car have 100,000+ miles on it runs great no rpm loss or exhaust smell.