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

Engine Coolant Temperature Sensor:

PURPOSE
Engine Coolant Temperature (ECT) Sensor is used to control:
- Exhaust Gas Recirculation (EGR)
- Fuel delivery
- Idle Air Control (IAC)
- Ignition Control (IC)
- Torque Converter Clutch (TCC)
- Cooling Fan control

OPERATION
The ECT sensor is a thermistor that is located in the engine coolant flow. Low coolant temperature sensor produces a high resistance 100,000 ohms at -40°C (-40°F). High coolant temperature, produces a low resistance 70 ohms at 130°C (266°F).

The Powertrain Control Module (PCM) sends a 5.0 volt signal to the ECT through a resistor in the control module and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot. Engine coolant temperature affects most systems controlled by the control module.

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.