The engine water coolant temperature sensor is a sensor that monitors the internal temperature of the engine. Coolant inside the engine block and cylinder heads absorbs heat from the cylinder heads when the engine is running. This sensor detects the change in temperature and signals the computer (PCM) so it can tell if the engine is cold, warming up at normal operating temperature or overheating. The water coolant temperature sensor is extremely important because the sensor’s input to the PCM affects the operating of the entire engine management system. Replacing this sensor would ensure an accurate temperature reading.