Quote:
Originally Posted by obeeone
Unfortunately they didn't go into detail about what exactly the rear O2 sensors do, but their exact quote was "Do not drive this MINI cat, the secondary sensors are needed for all kinds of measurement and you risk serious damage".
Then to just install the O2 back into its original position and uncheck the OEM Catted option box.
After reading numerous threads over on E90 post it's apparent that the rear O2 (narrow band) does monitor and provide feedback to the upstream (wideband) O2 which then adjust STFT and finally the LTFT.
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Ah OK. I am curious to know exactly how it is used, mostly because the DME probably expects it to have certain values based on having the OEM cat in place, and if you go catless or even aftermarket catted, the values it is seeing are going to be different, and as far as i know the tunes are not taking into account what type of cat you have or if catless, etc, aside from just the removal of the CEL. Kindof a long sentence i hope that made sense lol, but basically the DME would be seeing totally different values from the secondary O2 if you are catless vs. OEM cat, and i have not heard of the tunes accounting for that.
Also, narrrowbands are indeed quite accurate around 14.7:1 AFR but not really outside that range, so i question whether the secondary O2 is used at all during WOT situations.