Theory Of Operation
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The Powertrain Control Module (PCM) uses General Temperature Rationality to look at the outputs of the 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 the Intake Air Temperature (IAT) Sensor will be compared. If two sensors agree but not the third, the third sensor is declared as irrational. If all three sensors are irrational the General Temperature Sensor Rationality is declared.