1. Working principle of the coolant temperature sensor
The coolant temperature sensor is installed on the engine body or cylinder head and is in contact with the coolant. It is used to detect the engine circulating coolant. temperature, and transmits the detection results to the electronic control unit to correct the fuel injection amount and ignition timing. The water temperature sensor is often made of a thermistor that is very sensitive to temperature changes. Its structure and connection with the electronic control unit are shown in the figure. The two wires of the sensor are connected to the electronic control unit, and one of them is a ground wire. Thermistors often use negative temperature coefficient resistors. The lower the water temperature, the greater the resistance of the thermistor. Based on this signal, the electronic control unit increases the amount of fuel injection to increase the concentration of the combustible mixture.
2. Detection of cooling water temperature sensor
1. Resistance detection of cooling water temperature sensor
a. Car inspection
Generally, the ignition switch of a car will be in the OFF position. The car owner needs to disassemble the cooling water temperature sensor wire connector and use a digital high-impedance multimeter to test the resistance value between the two terminals of the sensor. . Its resistance value is inversely proportional to the temperature. Car owners need to note that it should be less than 1KΩ when the engine is hot.
b. Single-piece inspection
When the car owner performs a single-piece inspection, he needs to unplug the cooling water temperature sensor wire connector, and then remove the cooling water temperature sensor from the engine. Down. The car owner placed the removed sensor in the water in the water cup and heated the water in the cup. At the same time, use a multimeter to measure the resistance value between the two terminals of the water temperature sensor under different water temperature conditions, and compare the measured value with the standard value. If the comparison result does not meet the standards, the car owner needs to replace the water temperature sensor.
2. Detection of the output signal voltage of the cooling water temperature sensor
The car owner installs the cooling water temperature sensor and connects the connector of the sensor wire. When the ignition switch is in the “ON” position, then test the sensor output voltage signal from between the terminals of the water temperature sensor wire connector.
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