I did a diagnostic on my 2012 civic si sedan today for a check emission light. It ran the code p0420 which with my research seems to be a bad O2 sensor? I'm just making sure this is correct and what my option of fixing it would be. Thanks guys!
I did get it tuned but it came on after I got home from getting it tuned.That code is a catalyst efficiency below threshold code because the header you just installed has no cat. You can either get it fixed from a tune (which you should get any way) or try spark plug defoulers.
It's doing to make more noise being new. Lots of catless downpipe owners say it changes after some use. Nothing to do with o2We'll this morning I was driving and when I was down shifting my exhaust got extremely loud and vibrated underneath me, is this one of the symptoms of the o2 sensor not being cut off when he tuned it?