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Got it scanned and it's P0420: Catalyst efficiency below thresholdbank 1. They said it could be a bad catalytic converter or oxygen sensor. I borrowed a scanner and tried to measure the oxygen sensor readings over time.Sep 8, 2011
P0420 NISSAN - Catalytic Converter Efficiency Below Threshold Bank 1
The most common cause for the OBDII code P0420 on Nissan vehicles is the three way catalytic converter Bank 1 has reached the end of its useful life.. Since this is a very expensive part you need the code fully diagnosed as some other things like exhaust leaks or poor engine tune can cause it as well
misfiring can cause a P0420 code.
I would recommend a set of honda plug wires and plugs if the P0420 code returns.
I have used bolt in aftermarket bolt in catalytic converters but don't remember the brand name they fit ok and i have had 1 or 2 return with a P0420 code out of about 20. I have never replaced the oxygen sensor on a civic like yours.
I always fix the misfire problems, reset the computer, and have the customer drive it and see if the code p0420 returns. 50% don't have the P420 code return. drive it and see what happens and go from there.