Code 23, Manifold Air Temperature (Mat) Sensor Circuit Low Temperature Indicated: Notes

MAT sensor uses a thermistor to control signal voltage to the ECM. The ECM applies 4-6 volts on Gray wire 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.

1. Code 23 will set if signal voltage indicates manifold air temperature is less than -54°F (-48°C) for 2.7 seconds. This code will also set if an open exists in sensor or wire. This test determines if ECM and wiring are okay.
2. If resistance is more than 25,000 ohms, replace MAT sensor.