Theory Of Operation
WARNING: This page is about a different car, the 2016 Dodge Durango. However, it is still accessible from the selected car via links, so may be relevant.
The Coolant Temperature (ECT) Sensor 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, Engine Coolant and Intake Air Temperature Sensors will be compared. If the Intake Air and Ambient Air Temperature Sensors agree and the coolant temperature does not agree, the Engine Coolant Temperature Sensor is declared as irrational. If declared irrational a second comparison will be done after a short drive cycle.