Code 25, Intake Air Temperature High: Notes

ECM applies and monitors a voltage signal (4-6 volts) to MAT sensor. When manifold air is cold, sensor resistance is high and ECM sees a high signal voltage. As air warms, resistance decreases and voltage sensed by ECM drops. Sensor resistance can be measured at sensor terminals with harness disconnected.

1. This checks if code is a hard failure or an intermittent condition. Code 25 will set if monitored MAT sensor temperature is greater than 275°F (135°C).
2. This simulates conditions for a Code 23. If scan tester displays a low temperature, ECM and wiring are not at fault.