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

Voltage Versus Temperature Chart:

DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor that changes value due to temperature) mounted in the engine coolant flow. High coolant temperatures result in low resistance and low temperatures result in high resistance. The Powertrain Control Module (PCM) provides a 5 volt reference signal and a ground to the ECT sensor, and it measures the voltage signal as it changes due to the sensor's resistance.

OPERATION
A high coolant temperature will result in low signal voltage (near 0 volt) and low coolant temperature will result in high signal voltage (near 5 volts).

The ECT sensor uses two different temperature sensing circuits for two temperature ranges - below 50°C (122°F) and above 50°C. The PCM will shift between a high resistance circuit for low temps and a low resistance circuit for high temps.