The blower final stage fan resistor is known to fail. Symptoms are the heater fan speed varies regardless of the setting, the fan will not turn off when the car is switched off, or the fan will not switch on at all.
Average mileage: 94,284 (38,000–175,000)
18 people reported this problem
Blower fan would stay on or would not come on at all, would stay on even with key out. Stayed on all night one night. Purchased final stage resistor online and replaced it. First repair on the new car and all went well. If you have some patience and can maneuver yourself up under where you just removed the glove box and plate from, you should have no problems. Be careful of the air duct in the way and make sure you have something to grasp the old part with to wiggle it out of its spot. A T20 torx ratchet with extension, philips head bit and a a pair of kleins combined with about an hour and a half labor and all working perfect. Note: I have never replaced one before, never worked on a BMW and didn't own a torx bit. If you have patience and can read, there are a bunch of how to videos out there. One tip they didn't provide, that I will is when you attempt to 'wiggle' the old part out of the housing (after you have removed the torx screws), a good pair of linesman tools (I like Klein) will work to grab ahold of the electrical connector to wiggle it out with. Be gentle and controlled, but no need to worry about damaging the connector, you have the new all ready to go in.
On the hotest day in July I could not get my a/c to turn on. also the out side air temp was reading 40 degrees. I found a broken wire on the outside air temp probe. I repaired the wiring and cleaned the connector. the inside temperture began reading the correct temperture and the fan started working normally. So make sure your air temp probe is working.