DTC P0599-00: Thermostat Heater Control Circuit High: General Description
WARNING: This page is about a different car, the 2021 Kia Soul. However, it is still accessible from the selected car via links, so may be relevant.
A thermostat is a component of an HVAC control system which is installed in the coolant passage between engine and radiator and it blocks the coolant flow to the radiator until the engine is warmed up. When the engine is cold, no coolant flows through the engine. Once the engine coolant reaches operating temperature, the thermostat opens. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.