Theory Of Operation
WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
Engine Coolant Temperature Sensor performance looks at the outputs of three temperature sensors and compare them under cold start conditions. Following a start to run delay time, the outputs of the ambient, engine coolant, and intake air temperature sensors will be compared. If the intake air and ambient air temperature sensors agree and the engine coolant temperature does not agree, the engine coolant temperature sensor is declared as irrational.