Theory Of Operation
WARNING: This page is about a different car, the 2015 RAM 3500 HD and 2015 RAM 2500 HD. 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.