My car is throwing code P0420. What is the most likely cause, the oxygen sensor or the cat? I've got a high flow cat from Clear Image on the car right now. Any help would be appreciated. THanks.
It took me about 2 hours to do mine. I was working in my dad's garage, so I didn't know where exactly he kept all his tools, had to search around for every little thing. Anyways looks good.