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:
InspectionOperating Logic Test (Manual only)Inspect the PTC operation by confirmation logic as follows.1.Entering(1)Set the Floor mode and maximum heating position.(2)Turn off the blower switch.(3)Press the intake (recirculation) button 5 times or more.
Removal
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Put on gloves to prevent hand injuries.
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When removing with a flat-tip screwdriver or remover, wrap protective tape around the tools to prevent damage to components.