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

Engine Coolant Temperature (ECT) Sensor:

The Engine Coolant Temperature (ECT) sensor is a thermistor, a resistor which changes value based on temperature, mounted in the left cylinder head. Low coolant temperature produces a high resistance, 100,000 ohms at -38°C (-39°F), while high temperature causes low resistance 70 ohms at 130°C (266°F).

The Powertrain Control Module (PCM) supplies a 5.0 volt signal to the ECT sensor through a resistor in the PCM and measures the voltage. The voltage is high when the engine is cold. The voltage is low when the engine is hot. The PCM calculates the engine coolant temperature by measuring the voltage. The engine coolant temperature affects most systems the PCM controls.

The scan tool displays engine coolant temperature in degrees. When the engine starts, the engine coolant temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.

The engine coolant temperature and intake air temperature should be close to each other if the engine ha8 not been run for several hours, overnight. The following DTCs set when the PCM detects a malfunction in the ECT sensor circuit:
^ DTC P0117 ECT Sensor Circuit Low Voltage
^ DTC P0118 ECT Sensor Circuit High Voltage
^ DTC P0125 Excessive Time to Closed Loop
^ DTC P1114 ECT Sensor CKT Intermittent Low Voltage
^ DTC P1115 ECT Sensor CKT Intermittent High Voltage

Specifications contains a table in order to check for sensor resistance values relative to temperature.