Just bought a car from a NH dealership. When I bought the car it had no CEL on. On my way home it turned on. Took it to Autozone got it checked. The computer gave me exactly this:

P0420

Definition
catalyst system efficiency below threshold bank 1

Probable cause

1- a/f ration concern

2- Air leak near H02S(heated oxygen sensor)Bank 1

3-Ignition system concern

4-Faulty catalytic converter

What should I look at first??

 

If the CEL came on on your way home from the dealership, wouldn't the most obvious thing to do is to go back to the dealership and make them sort it out (free of charge, of course)?

-Lik

 

These ulev cars are known to foul out the cats. They just run too lean. The hybrids are extremely bad with this its what I'm dealing with.

 

I returned the car. Dealer is fixing .