ECM DTC EO38: Open Mat Sensor Circuit: Description

The MAT sensor is a thermistor, or variable resistor, that varies resistance based on temperature. The MAT sensor is a "Two-Wire" sensor with a reference, or signal, voltage coming from the ECM to sensor pin B (CKT 472), and a sensor reference ground on Pin A (CKT 476). As the temperature of the sensor increases, resistance decreases. As the resistance decreases, the signal voltage from the ECM decreases due to less voltage drop across the MAT sensor. High temperature will result in low signal voltage on CKT 472 and low temperature will result in high signal voltage on CKT 472. The ECM uses MAT information to correct the fuel delivery rate for the temperature of the air that is entering the intake manifold. Code EO38 sets when the ECM sees a low MAT reading when coolant is greater than -5°C.