Q: Bad O2 sensor

Hello, code P0420 represents right main catalyst deterioration. There can be a few things that need to be checked before replacing parts. The intake system needs to be inspected for vacuum leaks and unmetered air leaks. The exhaust system should be checked for leaks, from the exhaust manifolds all the way to the oxygen sensor after the catalytic converter. A scanner should be connected and the oxygen sensor. After, the car should be monitored for voltage activity, and test to see if it can be driven rich and lean. The mostly likely failed part is the catalytic converter,but some people believe in trying an oxygen sensor first. I would have a mechanic inspect your vehicle and let you know if you need a oxygen sensor or catalytic converter replacement.