Theory Of Operation
WARNING: This page is about a different car, the 2013 RAM 1500. However, it is still accessible from the selected car via links, so may be relevant.
The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The ECT Sensor functions as a typical two wire 5 volt sensor. The Powertrain Control Module (PCM) supplies 5 volts to the ECT Sensor signal circuit and supplies a ground to the low reference circuit. The Powertrain Control Module uses an internal voltmeter to read the signal circuit voltage which it then uses to calculate the engine coolant temperature.