O2 sensor operation
 

As far as I know on 2nd gens, the O2 sensor feedback is only used under cruise and light loads. But does anyone know if its used in all gears or only in 5th gear? Hence, is that the purpose of the 5th gear switch or is it used for emissions equipment? I'm speaking mostly of NA S5's but i believe all the 2nd gens work roughly the same in these regards. TIA