The exterior ambient air temperature sensor on a BMW 3 Series is located in the inner fender liner on the driver's side of the vehicle. Since the sensor is located underneath the bumper, it is prone to breakage and disconnection.
If the sensor gives false readings, a part of the sensor may be damaged or missing. Anything from flying road debris, such as rocks and gravel, to impact with concrete curbs can dislodge parts and cause sensor issues. Sensor covers, electrical connectors and device wiring are some of the most common parts to get damaged or go missing from a BMW's ambient temperature sensor.