Conditions for Setting the DTC
WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
The HVAC control module determines that the voltage applied to the input for the air temperature sensor is less than 0.09 V or greater than 4.9 V.