[TheTallJS]

If you put the climate control system on auto, it should detect if there are exhaust fumes and automatically switch in and out of recirculation mode, right? So where does the car detect this?

It's not the thing next to the cabin air filter; that's the outside air temperature sensor, right?

Any ideas?

Edit*

I quote from the website:
"Automatic Air Recirculation (AAC) delivers noticeably better air quality in the cabin of your BMW. The system recognises pollutants and contaminants in the outside air and removes them in a microfilter. Should the concentration of pollutants exceed a maximum level, the system automatically closes off air intake from outside and temporarily recirculates the air in the cabin."

[raceyBMW]

One of the sensors next to the cabin filter is the temp sensor, and the other is the quality sensor...I can't remember which is which, but its there.

[GMWNashville]

Auc sensor is on the right side when sitting in the vehicle-so the side your ebox is on. It does work to turn recirc on auto as long as recirc is turned on auto but you can still get some smells inside the car..just not as much if it wasn't on.