Code 25 - Mat Sensor Temperature High: Notes

The MAT sensor uses a thermistor to control the voltage signal to the ECM. The ECM applies and monitors a voltage signal (4-6 volts) to circuit No. 472. When manifold air is cold, the sensor resistance is high and the ECM will see a high signal voltage. As air warms, resistance decreases and voltage sensed by the ECM drops. Sensor resistance can be measured at ECM terminals "B5" and "W14".

Code 25 will set if a MAT temperature greater than 275°F (135°C) is sensed for more than 2 seconds. A Code 25 will also result if circuit No. 472 is shorted to ground.

1. This test checks to determine if the code is a hard failure or an intermittent condition.