Code 4: Air Mix Door Error
WARNING: This page is about a different car, the 2004 Suzuki Verona. However, it is still accessible from the selected car via links, so may be relevant.
This code will set if the output of the mix door indicator indicates that the door opening angle is out of range or does not change value when the door should be moving. This would indicate a short circuit or an open in the sensor or the associated wiring harness, a door motor that is not operating, or a malfunction of the ATC controller.