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

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

Code 25 will set if voltage input at ECM indicates an air temperature of greater than 277°F (136°C) for at least 3 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.