Circuit/System Description
WARNING: This page is about a different car, the 2009 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
The HVAC control module supplies the ambient air temperature sensor with a low reference circuit and 5-volt signal circuit. The HVAC control module determines the voltage drop across the sensor, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases. As the air temperature decreases, the sensor resistance increases.