Coolant Temperature Sensor/Switch (For Computer): Description and Operation

Figure 1:

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CIRCUIT DESCRIPTION
A thermistor built into the engine coolant temperature sensor changes the resistance value according to the engine coolant temperature.
A thermistor built in the sensor changes the resistance value according to the intake air temperature. The lower the intake air temperature, the greater the thermistor resistance value, and the higher the intake air temperature, the lower the thermistor resistance value (See Fig. 1.).
The intake air temperature sensor is connected to the ECM. The 5 V power source voltage in the ECM is applied to the intake air temperature sensor from the terminal THW via a resistor R.
That is, the resistor R and the intake air temperature sensor are connected in series. When the resistance value of the intake air temperature sensor changes in accordance with changes in the intake air temperature, the potential at terminal THW also changes. Based on this signal, the ECM increases the fuel injection volume to improve driveability during cold engine operation.