Greetings,

Can somebody please enlighten a novice as to the location of the "air quality sensor"? I thought it would be located in the vicinity of the cabin-air filter but I can't seem to find it. I'd like to be able to inspect and delicately clean it if it has been contaminated.

My recently acquired and already dearly loved vehicle is a 2007 A4 2.0 Quattro with tiptronic transmission.

Additional Info:
The A/C is stuck on recirculate - with the engine running, the A/C on Auto, and cabin filter removed the climate control intake duct louvers are fully closed. They only open if I switch the A/C to "ECON" or off or turn the car off.

Car is still under the factory warranty - but the nearest dealer is about an hour away (Phoenix AZ). Haven't acquired a VAG COM cable etc so I can't speak to any error codes.

I know the air quality sensor is a sensitive piece of equipment and if soiled etc can malfunction. The engine compartment of the car was detailed before I purchased the car and the dealer (non-AUDI) used a liberal amount of silicone / armor all / engine dressing. My fear is some of this fluid made contact with the air quality sensor. I know from my research that if the Air Quality sensor is contaminated or senses pollution (such as when in a tunnel or traffic) it will automatically force the A/C into recirculate so as to not pump pollutants into the cabin.

Assistance is appreciated and a Bentley manual is the first thing on my shopping list. Thanks in advance.