Pcm Code E038, Open Mat Sensor Circuit: Description
WARNING: This page is about a different car, the 1992 Cadillac Seville and 1992 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
MAT sensor is a thermistor that varies its resistance bases on temperature. As temperature of sensor decreases, sensor resistance increases. PCM Code E038 sets when PCM sees low voltage signal when coolant sensor temperature is 23°F (-5°C) or greater.