Engine Temperature Sensor: Description and Operation

The ECT sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low ECT produces a high resistance (100,000 ohms at -40°C/-40°F) while high temperature causes low resistance (70 ohms at 130°C/266°F).
The ECM supplies a 5-volt signal to the ECT sensor through a resister in the ECM and measures the voltage. The voltage will be high when the engine is cold, and low when the engine is hot.
By measuring the voltage, the ECM knows the engine coolant temperature. ECT affects most systems the ECM controls.
A failure in the ECT sensor circuit should set either a Diagnostic Trouble Code (DTC) 14 or DTC 15. Remember, these DTCs indicate a failure in the ECT circuit, so proper use of the chart will lead to either repairing a wiring problem or replacing the sensor, to properly repair a problem.