Code 25, IAT Sensor Circuit, High Temperature Indicated: Notes

Intake Air Temperature (IAT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across IAT sensor and converts it into a temperature reading. When outside temperature is cold, IAT sensor resistance is high. When outside temperature is warm, IAT sensor resistance is low. Therefore, when outside temperature is cold, ECM receives a high voltage input and when outside temperature is warm, ECM receives a low voltage input.

Code 25 will set when voltage input at ECM indicates air temperature greater than 284°F (140°C) for at least 5 seconds.

1. This test simulates Code 23. If ECM stores Code 23, ECM and its wiring are okay, and IAT sensor is faulty. If Code 25 resets, IAT sensor is okay, and wiring to ECM or ECM is faulty.