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

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 53 k ohms at -30°C (-22°F), while a high temperature causes low resistance of 177 ohms at 100°C (212°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 five-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. This sensor input is used by the PCM for fuel control, cooling fan control, ignition timing, EVAP canister purge control, idle speed control, and closed loop fuel control. The PCM also sends the coolant temperature information to the I/P cluster over serial data to indicate coolant temperature on the gage.

Engine Cooling Fan Control - The PCM controls operation of the engine cooling fan based on coolant temperature, air conditioning request, A/C pressure sensor input. Refer to Cooling System for a detailed description and operating criteria.

Hot Light Telltale - The hot coolant light telltale is used to indicate if there is a cooling system over-temperature condition. The light will illuminate on solid if the ECT senses engine coolant above 118°C (244°F).

Temperature Vs Resistance:

The following chart lists the resistances of engine coolant temperature sensor as compared to temperature.