Hyundai Ioniq (AE): Engine Control System / Engine Coolant Temperature Sensor (ECTS). Description and operation
Engine Coolant Temperature Sensor (ECTS) is located in the engine coolant passage of the cylinder head for detecting the engine coolant temperature. The ECTS uses a thermistor that changes resistance with the temperature.
The electrical resistance of the ECTS decreases as the temperature increases, and increases as the temperature decreases. The reference +5V is supplied to the ECTS via a resistor in the ECM. That is, the resistor in the ECM and the thermistor in the ECTS are connected in series. When the resistance value of the thermistor in the ECTS changes according to the engine coolant temperature, the output voltage also changes.
During cold engine operation, the ECM increases the fuel injection duration and controls the ignition timing using the information of engine coolant temperature to avoid engine stalling and improve drivability.

Inspection1.Turn the ignition switch OFF.2.Disconnect the IATS connector.3.Measure resistance between the IATS terminals 3 and 4.4.Check that the resistance is within the specification.
Specification
Temperature
Resistance (kΩ)
°C
°F
-40-4048.
Other information:
Component Location1. Blower unit assembly Components1. Duct Seal2. Intake duct case3. Air intake door assembly4. Intake door5. Seal6. Intake duct case (A)7. Air filter cover (A)8. Intake actuator9. Air filter cover10. Air filter 11. Blower unit pad12.
Removal1.Disconnect the negative (-) battery terminal.2.Remove the tailgate lid trim.(Refer to Body - "TailGate Lid Trim")3.Disconnect the Rear view camera connector (A).4.Remove the Rear view camera assembly after loosening the mounting screws.Installation1.