The Nissan Path

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.

There are a number of things that can cause a catalyst code, including worn spark plugs, failing ignition coil, bad gas, improper fuel pressure, too lean or too rich mixture and exhaust leaks. Another common reason is the converter substrate becomes inefficient at breaking down the exhaust gases. It is usually when an engine is not running correctly that it caused the substrate to break apart. If the substrate is simply inefficient, it usually isn't an issue. The issue of converters breaking down and having debris get sucked into the combustion chambers has happened, but it is pretty rare on the whole. Of course, if you want to be pro-active and eliminate that chance, then replace the catalytic converter if it is found to be faulty.