So driving home today I got a check engine light, tested it and it came up p0420 catalyst efficiency, however I have Berk test pipes on the car . I checked the Nissan site to see what they said (which was bad plugs or a bad o2 sensor), and the car has new ngk plugs as of 3 days ago, and the bank one o2 sensor is also new from a few weeks ago. Ideas anyone? thanks

 

it means that your cat isnt changing the exhaust composition enough to pass the test

 

I ran 2x o2 extenders for each o2 after my test pipes and did not throw a code

 

Its throwing the cat inefficiency code because the cats aren't there... Test pipes usually throw that code. Get an Uprev tune