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

Coolant Temperature Sensor:

Used by the fuel injection and ignition ECU:

PURPOSE
The coolant temperature sensor (located front of engine, under intake manifold) provides the ECU with information regarding the engine temperature necessary for proper adjustment of injection duration.

DESIGN
The coolant temperature sensor is of the NTC (negative temperature coefficient) type. This means the higher the coolant temperature, the lower the sensor resistance.

OPERATION
The ECU applies a regulated constant voltage to the sensor, and monitors the voltage in the circuit. As temperature increases, sensor resistance decreases, causing a decrease in the measured voltage of the circuit. By monitoring the circuit voltage, the ECU can calculate the engine temperature, and adjust the air/fuel ratio and ignition timing to meet the specific demands of the engine, at that temperature.