Quick O2 sensor question - rears only for emissions testing?
So we do OBDII testing in Colorado - I'm reading about the different types of headers, and just want to ask a quick clarification question - the rear O2 sensors, are they used for A/F ratio or closed loop ops at all, or only for emissions verifying that the cats are working?
I don't want to program out something that is actually doing something for maintaining engine tune, but if it's just checking for the emissions systems, I don't care so much, if you know what I mean.



