DTC B1687-88: Engine Coolant Temperature Sensor Fault - CAN Signal: General Description
WARNING: This page is about a different car, the 2024 Kia Sorento. However, it is still accessible from the selected car via links, so may be relevant.
In case of engine cold start, the air conditioner control module receives engine coolant temperature sensor signal through the CAN signal and the mode is changed to defrost by controlling the mode actuator.