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

Engine Coolant Temperature (ECT) Sensor:

ENGINE COOLANT TEMPERATURE (ECT) SENSOR
The engine coolant temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. A low coolant temperature produces a high resistance (100,000 Ohm at -40°C/-40°F) while high temperature causes low resistance (70 Ohm at 130°C/266°F). The PCM supplies a 5 volt signal to the 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 calculates the ECT. The scan tool displays the ECT in degrees. After engine startup, the temperature should rise steadily to about 90°C (194°F) and then stabilize when the thermostat opens. If the engine has not been run for several hours (overnight), the ECT and Intake Air Temperature (IAT) displays should be close to each other.

The ECT affects most systems the PCM controls. A hard fault in the ECT sensor circuit should set DTC P0117 or DTC P0118; an intermittent fault should set a DTC P1114 or P1115. For sensor resistance values relative to temperature refer to Temperature vs Resistance.