role of post-cat O2

[kimiraikkonen]

I know some people have mentioned that the post-cat O2 sensors are for only monitoring O2 differentials across the cat (i.e., only to detect if you have a failing cat)............

But then have heard others mention that the post-cat O2 provide other trim level inputs that are used by the ECU to adjust overall fuel ratio, etc.

Am approaching 120K mi and had replaced my front 02 sensors at 95K when I had a O2 failure code. No codes right now but did see that note in the manual recommending O2 sensors being replaced at 120K...and assumed that meant the rear O2 sensors as well.

Wanted to see what others are doing.

[ItsGary]

PreCat O2s is for AFR
PostCat O2 is for monitoring