DTC P1521-00: Engine Coolant Temperature Sensor Circuit High (EHRS): 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.
The Exhaust Heat Recovery System (EHRS) uses the exhaust heat that is discarded after engine combustion to heat the coolant during engine start or in cold weather and improve fuel efficiency. When the engine is heated enough, the EHRS opens the valve on the exhaust gas channel to block the heat exchange between exhaust gas and coolant to prevent overheating of the coolant. Valve on the exhaust gas channel is opened or closed by the wax actuator depending on the coolant temperature.
A separate water temperature sensor is mounted to monitor the coolant temperature. When the coolant is overheated (120°C (248°F) or above), the engine overheat warning lamp turns on the cluster.