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

Engine Coolant Temperature Sensor:

PURPOSE
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperature 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).

OPERATION
The Powertrain Control Module (PCM) supplies a 5 volt signal to the ECT sensor through a resistor in the PCM 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 PCM calculates the engine coolant temperature. Engine coolant temperature affects most systems the PCM controls.
A failure in the ECT sensor circuit should set either a Diagnostic Trouble Code (DTC) 14 or DTC 15. Remember, these DTC(s) 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.