Hyundai Sonata LF: 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.

Inspection
1.
Connect a GDS on the Data Link Connector (DLC).
2.
Measure the output voltage of the BPS at idle and IG ON.
Specification: Refer to "Specification"
Removal
1...
Other information:
Inspection
1.
Turn the ignition switch OFF.
2.
Disconnect the HO2S connector.
3.
Measure resistance between the HO2S terminals 2 and 5 [B1/S1].
4.
Measure resistance between the HO2S terminals 3 and 4 [B1/S2].
5.
Check that the resistance is within the specification...
S..