BMW External Air Temperature Sensor (OBC) -40, -22, etc. E39, E36, etc.
This answer is applicable for many BMWs in addition to the one listed below.
car year: 2002
car model: 525i
After a snowstorm drive my sensor in the dash reads -40 all the time. What could be wrong? i wonder if it’s become disconnected. Where do I find the outside sensor to look?
You likely either have a faulty exterior temperature sensor, the sensor has come unplugged or the sensor is missing altogether. If the sensor is missing, it would not be uncommon for the harness plug to be ripped from the vehicle’s wiring as well. We do carry all of the various model temperature sensors and we have plug repair kits for some of them.
E36 chassis (3-series 92-98):
On the E36 chassis, the sensor is located in the passenger side brake cooling duct. You can see it projecting into the duct, by looking into the duct from the front (assuming it has not been knocked out). To replace the sensor, you must access it by removing the under bumper splash shields. See the link above for the Winter 2007/2008 Fast Times, which shows a photo of the location.