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 functions as a normal two wire, 5 volt sensor. The PCM supplies the ECT Sensor with a 5 volt reference and a filtered ground (return) circuit. For the ECT Sensor diagnostic, the PCM internally monitors the voltage on the signal circuit, which is converted into a temperature reading. If the voltage reads above the high calibrated threshold, or below the low calibrated threshold, a circuit high or low fault is set.