Need to figure out what this part does

[rubbster]

On the 95 e38 740i there is a black box located on the lower right of the fan shroud. One connector into it. What does this do? Possibly control the such fan? Unfortunately it feel of my shroud into some coolant I drained so I beloved I need to replace it.

Thanks!

[psjr]

That is the AUC sensor. It senses airborne pollutants in order to determine when to turn on recirculation if you have the automatic recirculation mode (AUC) turned on.

EDIT: Great post from Q: http://www.bimmerfest.com/forums/showpost.php?p=5532757&postcount=10