Coolant Temperature Sensor/Switch (For Computer): Description and Operation
PURPOSE / OPERATIONA thermistor built into the engine coolant temperature sensor changes the resistance value according to the engine coolant temperature. The lower the coolant temperature, the greater the thermistor resistance value, and the higher the coolant temperature, the lower the thermistor resistance value.
The engine coolant temperature sensor is connected to the ECM. The 5.0 volt power source voltage in the ECM is applied to the engine coolant temperature sensor from the terminal THW via a resistor R.
That is, the resistor R and the engine coolant temperature sensor are connected in series. When the resistance value of the engine coolant temperature sensor changes in accordance with changes in the engine coolant 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.