A coolant temperature sensor is confined to the engine of a vehicle and measures the temperature of the vehicle¡¯s engine coolant. The sensor feeds this information back in the form of an electrical current to the engine control unit (ECU). The ECU then responds to a change in the temperature difference and readjusts the engine¡¯s fuel injection.
A coolant sensor is similar to a thermistor, based on the working principle that a change in electrical resistance will be the direct product of a change in the temperature of a wire carrying current. With a coolant temperature sensor, the full sensor is located in a coolant passage that sits before a thermostat and is connected to the engine control and monitoring unit.
The coolant temperature sensor is fastened to the intake manifold of an engine coolant and is often referred to as a negative temperature coefficient type of sensor. In terms of resistance capacity, this coolant sensor has 20,000 ohms at 248 degrees Fahrenheit. There is an inverse relationship between the electrical resistance and the engine coolant (i.e. when the engine coolant temperature increases, the electrical resistance decreases and this also causes a voltage drop in the sensor).
A basic functional principle to a coolant temperature sensor begins with the ignition switch. When the ignition switch is ¡®on¡¯, a voltage passes through the resistor and heats it up. The resistor is connected to an electrical grid that behaves like a data logger measuring the temperature difference of the resistor.
In the event of air traveling through a vehicle engine, which can come as a result of heavy acceleration, the resistor to the sensor starts to cool down and drops its resistance charge. To control and maintain a balance in the engine temperature, the coolant sensor detects the drop in electrical resistance and emits a voltage to the resistor, a process that is completed in the space of a millisecond.
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