Hey Guys, scanned my car this morning as my CEL came on and got code P2181. The Bentley site says "P2181 Engine coolant heater failure, Engine coolant level is too low, Thermostat failure."
I have checked the coolant level and it is full. Of the remaining 2 choices, in your experience, which is most likely to be the culprit? I will replace the thermostat myself if necessary, but am not sure what the engine coolant heater is.

Thanks for your input and assistance.