Code 25, Manifold Air Temperature (Mat) Sensor (Temperature Too High): Notes

The MAT sensor uses a thermistor type resistor to control signal voltage to the ECM. A 4-6 volt reference signal is supplied to the sensor on circuit on circuit No. 472. When manifold air temperature is cold, sensor resistance is high and the ECM will see a high signal voltage. As the manifold air temperature rises, sensor resistance becomes less and voltage drops.

Test Number 1)  This step checks if Code 25 is a result of a hard failure or an intermittent condition.

A Code 25 will set if:

• Signal voltage indicates a MAT temperature greater than 275°F (135°C) has been detected for longer than 2 seconds.