The Nissan Path

So the P0430 P0420 codes are pretty constant. I will clear them and then they come back after a day or so. Engine runs smooth, no loss of mpg, no rough idle, just the codes. I put new O2 sensors on both sides with non foulers and that worked for a few weeks, but codes came back. This last year I have only been using non-ethanol fuel for every fill up. My local exhaust shop says I shouldn't replace both cats if it's not causing any problems unless I want to pay that much just to clear the check engine light.

Any ideas on what to do? I've done seafoam treatment several times as well.

It's funny how some R51's go through catalytic converters and some don't. My 2006 with 170,000 miles has had both fronts replaced in its lifetime. The left bank was replaced at 84,000 miles and now it is due again for replacement. Meanwhile, my 2008 model has 227,000 miles and still has the originals without any issues. Assuming there is not an engine performance issue (running too lean or too rich or misfiring) and there are no intake or exhaust leaks, the only thing you can do which you haven't done already is bite the bullet and replace the upstream converters.