Engine Coolant Temperature (ECT) Sensor

Voltage Versus Temperature Chart:

The Engine Coolant Temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The ECT sensor resistance varies from 100,000 ohms at -40°C (-40°F) to 70 ohms at 130°C (266°F). The PCM uses the ECT signal to calculate the coolant temperature. The PCM applies 5 volts to the ECT signal circuit through a pull-up resistor. When the engine coolant temperature is cold, the ECT sensor resistance is high. This causes the PCM to detect a high ECT signal voltage. When the engine coolant temperature increases, the sensor resistance lowers. The PCM should detect a low ECT signal voltage

The scan tool displays the engine coolant temperature in degrees. After engine startup, the coolant temperature should steadily rise to approximately 90°C (194°F). Then, when the thermostat opens, the temperature should stabilize. If the engine has not been run for several hours (overnight), the ECT sensor and IAT sensor scan tool displays should read close to each other. Engine coolant temperature affects most PCM controlled systems. A hard fault in the ECT sensor circuit should set DTC P0117 or P0118. An intermittent fault should set DTC P1114 or DTC P1115. To check ECT sensor resistance relative to temperature, refer to the Temperature Vs Resistance table. [1][2]Computers and Control Systems