So, you have the dreaded P0420 or P0430 code. Aren’t you lucky???
These are catalytic converter efficiency codes, and almost always they are caused by a bad catalytic converter. Key word is almost.
These things are expensive! AND if you get the wrong one you can fail for that too!
There is a lot of talk about additives to help clean this out, but it is a gamble.
You should have the vehicle diagnosed to make sure, but chances are high it will need a catalytic converter.
I realize that the internet is rife with suggestions of replacing the rear oxygen sensor, but personally I have never, ever, seen it cure one of these codes, and I have been playing the game for over 45 years.
If you want us to diagnose this code for you, then give us a call at 916-266-1821