Can anyone tell me if the cabin air sensor intake fan inside the interior light housing of my 2001 C220 cdi should remain on at all times whether the engine is running or not? I recently was left with a flat battery after a three day break from driving and on investigation noticed that the fan stayed on continuously. It does however seem to make an attempt at stopping when I lock myself in the car but starts up again straight after it stops. Any help would be much appriciated.

 

"cabin air sensor intake fan inside the interior light housing" This is a new one on me! I plead the fifth!

 

I had a similar arrangement on my BMW730i where the air is sucked from the passenger compartment and blown over a temperature sensor that controls the heating or cooling. The BMW version was only on when the main heating fan was on. This one however, seems to have it's own agenda! It is located diectly under the small grill next to the main interior light.

 

The blower should not run with the key off. According to the test procedure, the key must be on to test it. Have you used a piece of paper to test it to verify the aspirator blower is what is running after locking?

 

Thanks for the reply. Yes I just tried the paper trick and it is definitely pulling air through the vent at all times. The hesitation only happens when the doors are locked (it's just amazing how still you have to sit inside to prevent the alarm from going off!!). There seems to be a click at this point similar to a very tiny relay tripping but it may just be a liitle slack releasing on the fan bearing. Any ideas apart from a new interior light unit? Thanks again for your comments.