Circuit/System Description
WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.
The B39 Air Conditioning Evaporator Air Temperature Sensor is a 2-wire negative temperature coefficient thermistor.
The sensor operates using signal and low reference circuits. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor sends a signal voltage between 0 - 5 V. If the BCM detects a malfunctioning sensor the software uses a default air temperature value. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.