PhotoJ

Was having issues with my 2000 1.8 Sentra. SES light was on - code read "cylinder 1 misfire" Changed coil and it smoothed out. Drove for about 200 miles and now SES ligh is back on - engine seems to idle smoothly but while driving feels like a three-legged-dog.

Went to the SAM Kiosk and it coded with P0420 - mentions catalytic converter and O2 sensors as possible problems - Specifically it says "Catalyst System Efficiency below threshhold (Bank 1) - does this seem to be a catalytic converter or an O2 sensor issue. If it sounds like an O2 sensor - is it possible to determine which one of the 4 it would be?

Any help would be appreciated - car needs to be inspected soon - like this month.

Thanks in advance!

Doja

ive allready answered this one here on the forums. but here goes..I have the same exact car as you and with only 60k on the odometer I had the same code. It takes a while for this one to set usually, if you clear it. I actually got some brand new cats installed from the dealer under the 8 year 80k fed emissions warranty. At the dealer I went to you had to have this code on in order for the work to be done. If you arent covered under warranty, then I would suggest you make sure the 02 sensor(s) is bad before changing them. You can make sure at any reputable shop that has a scan tool (not a code reader)
that the voltage from the 02 sensors is switching from 0ish to about 1volt. IF your cat is bad dont go to the dealer out of warranty, you will pay out the a$$ for nissan parts. Instead just go to a local muffler shop. Your welcs.
if your car was missfiring for a long time and fuel was being dumped into the cat for a while its likely the cat was damaged.

PhotoJ

Thanks for the input. Just got my New Beetle back on the road after a long battle with similar issue - replaced the cat with an after-market and it is doing fine. I have replaced the cat once on this sentra under warranty. I will be looking for an after market now. I think i hosed the cat when the cylinder 1 coil was dead and running unused fuel out the backdoor. Thanks again