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

ECT Circuit (Typical):

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)

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 control module 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.

The control module uses information from the ECT to calculate spark advance as follows:
- Cold engine results in more spark advance.
- Hot engine results in less spark advance.