Gasoline Engine Water Temperature Sensor/ Intake Air Temperature Sensor


The water temperature sensor and intake air temperature sensor have builtin thermistors for which the lower the temperature, the larger the resistance value and, conversely, the higher the temperature, the lower the resistance value. And this change of the thermistor resistance value is used to detect the changes in the coolant and intake air temperatures. As shown in the illustration, the built-in resistor in the engine ECU and the thermistor in the sensor are in connected in series in the electric circuit so that the signal voltage detected by the engine ECU changes in accordance with the changes in the thermistor resistance. When the temperature of the coolant or intake air is low, the thermistor resistance becomes large, creating a high voltage in the THW and THA signals.
1. Water temperature sensor
The water temperature sensor measures the temperature of the engine coolant. When the engine coolant temperature is low, the idling must be increased, the injection duration increased, the ignition timing angle advanced, etc., to improve drivability and to warm up. For this reason, the water temperature sensor is indispensable for the engine control system.
2. Intake air temperature sensor
The intake air temperature sensor measures the temperature of the intake air. The air amount and density changes according to the air temperature. Therefore, even if the air amount detected by the air flow meter is the same, the amount of fuel that is injected must be corrected. However, hot-wire type air flow meter directly measures the air mass. Therefore, the correction is not required.

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