quick o2 sensor question and why

more than likely, no. as they age, they simply fluctuate more slowly and with less extreme (they dont have the range they once did). they shuttle from ~0 -1.0 volt.

if they go far enough south that they arent working, a code should be tossed and the puter will disregard their input.

my two cents (I'm no JR or Yount). :)