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

The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor that changes value based on the temperature) mounted in the engine coolant stream. Low coolant temperature produces a high resistance (100,000 Ohms at -40°C/-40°F) while high temperature will cause a low resistance (70 Ohms at 130°C/266°F).

The PCM supplies a 5 Volt signal to the Engine Coolant Temperature (ECT) sensor through a resistor in the PCM and measures the voltage. The voltage is high when the engine is cold and low when the engine is hot. By measuring the voltage, the PCM knows the engine coolant temperature. The engine coolant temperature affects the fuel control and the glow plug system.