Code 25, Manifold Air Temperature (Mat) Sensor Circuit Low Temperature Indicated

MAT sensor uses a thermistor to control signal voltage to the ECM. The ECM applies 4-6 volts on circuit No. 472 to the sensor. When manifold air is cold, sensor resistance is high, this means ECM will see high signal voltage. As air temperature warms, sensor resistance becomes less and voltage drops.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Code 25 will set if signal voltage indicates manifold air temperature is less than -31°F (-35°C), engine has run for one minute or longer and vehicle is not moving. This code will set from an open sensor, wire or connection. This test will determine if ECM and wiring are okay.
If resistance is more than 25,000 ohms, replace sensor.

Fig 1: Code 25, Circuit Wiring Diagram & Flow Chart

Courtesy of GENERAL MOTORS CORP.