I have been getting an intermittent engine code (420) for about 2 years now. I will reset, then it may go 6 months before coming on again; it is my perception that it typically comes on more in wet/slushy weather. I believe this is related to the catalytic convertors (one side was replaced under warranty at 50,000 km). The mileage is currently at 160,000 km. There doesn't seem to be any impact on mileage or power, but I'm worried that a failing CAT could cause engine damage with debris through the manifold.
Any thoughts or advice would be appreciated.