Apparently the MXP 02 housing won't throw a CEL. It has some type of catalytic "screen" in the 2nd 02 bung.
http://www.gencoupe.com/genracer/49618-mxp-o2-housing-pre-install-review.html#post542339
http://www.gencoupe.com/genracer/49618-mxp-o2-housing-pre-install-review.html#post542339