P0421 Check Engine Light Fix "2001 Mazda protege 2.0 ES" (make not important!)

Getting rid of check engine light for code P0421. The real fix would be anywhere from $300-$1000 and that would be a new catalytic converter i beleive (not a mechanic). My car was 2001 Mazda Protege 2.0 ES. I just passed smog with this trick but i want to say it is just tricking the computer not actually fixing anything.I suggest only using this in case you need to pass smog and don&have a grand to drop on a cat.