so I just got a high flow resenator along with a catback exhaust and a day later my check engine light pops up with the code P0420 (M) 1/1 Catalytic Converter Efficency Catalyst 1/1 efficency below required level anyone know why???????thanks

 

do the nonfouler trick

 

how is that done?

 

P0420 (M) 1/1 Catalytic Converter Efficency Catalyst 1/1 efficency below required level , sounds like you got what you asked for.