I just picked up a 2011 R57 am getting a P0597 Thermostat Heater Control. My problem is, I have a sending unit? that I can't find in any parts diagram and the wires going to it are missing. Maybe someone can identify it for me and possibly tell me where it is in the parts charts. I have circled the part in the picture.

 

The part you're referring to is likely the thermostat itself or the thermostat housing, which includes the heater control. This component can sometimes have a sending unit or sensor that monitors temperature and controls the heater circuit.