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

Voltage Versus Temperature Chart:

The ECT sensor is a thermistor (a resistor that changes value due to temperature. High coolant temperatures result in low resistance and low temperatures result in high resistance. The 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 sensors resistance. 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 circuit uses two different temperature sensing circuits for two temperature ranges - below 50°C (122°F) and above 50°C (122°F). The PCM will shift between a high resistance circuit for low temperatures and a low resistance circuit for high temperatures.

The PCM uses ECT information for fuel enrichment, ignition control, canister purge control, idle speed control and Closed Loop fuel control. A faulty ECT sensor may cause various driveability conditions and should set a PCM Trouble Code.