The MAT sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (about 4-6 volts) on CKT 472 to the sensor. When the manifold air is cold the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. As the air warms the sensor resistance becomes less, and the voltage drops.
Code 25 will set if:
A Scantool reads temperature of the air entering the engine and should read close to ambient air temperature when engine is cold, and rises as underhood temperature increases.
Check harness routing for possible short to ground in CKT 472.
Does scantool display MAT 145 C or hotter?