So I got the po420 error code. I had one of these a while back - one fixed with a computer flash, the other needed a new Cat and o2 sensor that the dealer replaced under warranty.

I received another one, just today. I imagine that the cat is going, again, along with the o2 sensor. Does anyone know how long these parts are under warranty from Mazda?

Thanks

 

The cat has to last 100,000 miles

 

Emission related stuff has a lot of miles.

So replace them, its free.