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

Engine Coolant Temperature Sensor:

DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) immersed in the engine coolant stream. The coolant temperature sensor provides the Powertrain Control Module (PCM) with information regarding coolant temperature.

OPERATION
The Powertrain Control Module (PCM) supplies a 5 volt signal to the ECT 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 knows the engine coolant temperature. engine coolant temperature affects most systems the PCM controls.

The scan tool displays engine coolant temperature in degrees. After engine startup, the temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens. If the engine has not been run for several hours (overnight), the engine coolant temperature and intake air temperature displays should be close to each other. When the PCM detects a malfunction in the ECT sensor circuit, the following DTCs will set:
^ DTC P0117 circuit low.
^ DTC P0115 circuit high.
^ DTC P0125 excessive time to Closed Loop.
^ DTC P1114 circuit intermittent low.
^ DTC P1115 circuit intermittent high.

See Specifications for a table of sensor resistance relative to temperature.