Code 25: Mat Sensor Temp To High: Notes

The manifold air temperature sensor (MAT) uses a thermistor to control the signal voltage to the ECM. The ECM applies 4-6 volts to circuit No. 472 and on to the MAT sensor. When 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.

1. This check determines if Code 25 is the result of a hard failure or an intermittent condition. A Code 25 will set if the following conditions occur:
   • Engine has been running longer than 8 minutes.
   • A MAT temperature is more than 135°C detected for a time longer than 2 seconds.
   • VSS signal is present.