Theory Of Operation

The Intake Air Temperature (IAT) Sensor rationality diagnostic looks at the outputs of three temperature sensors and compares them under cold start conditions. Following a start to run delay time the outputs of the Ambient Air Temperature (AAT) Sensor, Engine Coolant Temperature (ECT) Sensor, and Intake Air Temperature (IAT) Sensors will be compared. If the ECT and AAT Sensors agree and the IAT Sensor does not agree, the IAT Sensor is declared as irrational. If declared irrational a second comparison will be done after a short drive cycle.