Engine Coolant Temperature (ECT) Sensor

The Engine Coolant Temperature (ECT) sensor (1) contains a semiconductor device that changes resistance based on temperature (a thermistor). The ECT sensor is located in the coolant crossover pipe at the center rear of the engine. The ECT sensor has a signal circuit and a ground circuit. The ECM applies a voltage to the sensor (about 5.0 volts) on the signal circuit. The ECM monitors changes in this voltage caused by changes in the resistance of the sensor in order to determine the engine coolant temperature. When the engine coolant is cold, the sensor (thermistor) resistance is high, and the ECM's signal voltage is only pulled down a small amount through the sensor to ground. When this occurs, the ECM senses a high signal voltage (low temperature). When the engine coolant is warm, the sensor's resistance is low, and the signal voltage is pulled down a greater amount. This causes the ECM to sense a low signal voltage (high temperature).

This voltage is used to determine:
^ The injection time for pre-injection
^ The injection time for cold starting and warm-up enrichment
^ Engagement of closed loop
^ The idling speed
^ The ignition timing during warm-up and knock control

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 the 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 ECM detects a malfunction in the ECT sensor or circuit, the following DTC(s) will set:
^ DTC P0115 Engine Coolant Temperature (ECT) Sensor Circuit
^ DTC P0116 Engine Coolant Temperature (ECT) Sensor Performance