2000 V40, Code P0420

[jcartermedia]

Hey all!

Just had a code come up on Tuesday evening while I was coming home - P0420 Catalyst system below Efficiency Threshold (Bank1). I did some research and it seems to be the catalytic converter, specifically "Bank 1" being the front O2 sensor. The car runs just fine other than an occasional RPM dip that I've been experiencing for a little while (also posted about this a little while ago). I'm still trying to followup on the advice I got regarding that.

I also did see another topic on here(through a Google search) from December 9, 2006 about the same code on an S40T. They got these "possibilities" from the person who ran their codes (#1 being most likely):

1. Catalytic Converter; Really hoping it's not this as it seems to be pretty spendy to fix. I saw in the other post from 2006 that if the Cat was bad, I would smell rotten eggs which I haven't. There was a sort of smell of rotten eggs when it was misfiring but, hasn't been at all since that was fixed.
2. Engine Misfire, or running problem; It was misfiring a couple months ago but, that was taken care of and hasn't since.
3. Large Vacuum Leak; Not positive here. I did put gas in it the other day... I re-tightened the gas cap this morning and am hoping that was all it was?
4. Engine Oil leakage into Exhaust Valve Guide Seals; I am aware of an oil leak somewhere in the system, just don't have the budget to take care of it quite yet.

Since the car seems to be running fine - no significantly noticeable loss of power, thick exhaust, or unusual smells - I'm curious how important this code is. In another forum, someone suggested this problem may be caused by it being so cold and web out recently (a little north of Seattle)..??