Coolant Temperature Sensor/Switch (For Computer)

Voltage Versus Temperature Chart:

The PCM supplies a 5 volt reference signal and a ground to the ECT signal to the PCM. A high coolant temperature will result in low signal voltage (near 0 volts) 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 and above 50°C. The PCM will shift between a high resistance circuit for low temps and a low resistance circuit for high temps.