Failed Engine Cooling Thermostat
Engine Cooling Thermostat harness is open or shorted
Engine Cooling Thermostat circuit poor electrical connection
Engine Light ON (or Service Engine Soon Warning Light)
The Engine Control Module (ECM) controls the Pulse Width Modulated (PWM) thermostat. The engine coolant thermostat heater controls coolant flow and regulates the engine operating temperature. The ECM supplies 12 V to the thermostat. The ECM controls the engine coolant thermostat heater by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled-up to a voltage. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.