Originally posted by zuulmusic:
I was very careful with my sensor and I set the same 420 code with my hi-flow cat. After researching the issue, multiple sources told me it was because of the hi-flow cat. The computer's sensitivity for that is pretty high. I had the car emissions checked (long story for why they sniffed the exhuast instead of OBD2-ing it), and my car passed with flying colors, even with the 3" downpipe and hi-flow cat.
$10 says your new O2 sensor will give you the same code over time I've been driving with my 3"dp and high flow cat for a year now. Never thrown a code.