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

Temperature - Resistance Chart For Sensors:

Purpose:
This sensor input is used by the PCM for fuel enrichment, ignition timing, EGR operation, canister purge control, idle speed control, and Closed Loop fuel control.

Operation:
The engine coolant temperature (ECT) sensor is mounted in a coolant passage located in the cylinder head. The engine coolant temperature sensor is a thermistor-type sensor. A thermistor resists the flow of electricity similar to a resistor. However, the resistance of a thermistor increases as the temperature drops. For example, at a low air temperature a thermistor produces a high resistance of 93k ohms at -40°C (-4°F), while a high temperature causes low resistance of 65 ohms at 140°C (248°F).

The engine coolant temperature sensor is a two-wire sensor that receives a reference signal voltage from the PCM to sensor pin B and a sensor reference ground from the PCM to sensor pin A.

The PCM supplies the 5-volt reference signal to the engine coolant temperature sensor through a current-limiting resistor located inside the PCM. The signal received by the PCM indicates the temperature of the engine coolant, which is an indication of engine operating temperature.