Just curious if anyone has fixed a p0420 error. I have 143k miles and it throws the code every so often. Should I go with replacing sensors first or go and replace the cat. I don't notice any signs of a bad cat, and the guy I bought it from said he was monkeying around with the sensor before I got it .

 

I have 2013 XC60 T6 check engine on. Dealer wants to replace Cat Conv and front and back O2 sensors $4,500. Parts seem much cheaper but other exhaust shops wont use non-volvo parts?