Monitor Description

WARNING: This page is about a different car, the 2004 Lexus ES 330. However, it is still accessible from the selected car via links, so may be relevant.

The engine coolant temperature (ECT) sensor is used to monitor the engine coolant temperature. The ECT sensor has a thermistor that varies its resistance depending on the temperature of the engine coolant. When the coolant temperature is low, the resistance in the thermistor increases. When the temperature is high, the resistance drops. The variations in resistance are reflected in the voltage output from the sensor. The ECM monitors the sensor voltage and uses this value to calculate the engine coolant temperature. When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault in the ECT sensor and sets a DTC.

Example:

When the ECM calculates that the ECT is -40°C (-40°F), or more than 140°C (284°F) and if either of the conditions continues 0.5 second or more, the ECM will set a DTC.