What are these? And do they relate to a p0599 error code? 2009Aveo5

[Drunen]

Arrow to front of Car, picture is from below passenger side.
On a hot day the check engine light came on with a p0599 Thermostat Heater Control Circuit High error. My coolant was a tiny bit below the minim level so I added some and looked for leaks. There seemed to be some coolant build up(or maybe just grease) under the belt units (sorry I'm not sure what they are either) on the passanger side. I lifted the car and took some pictures. My first thought was this was a temperature sensor that needed to be replaced and that would clear up my p0599 but it doesn't match pictures I found on other threads about replacing it. Also, I have a loose grease caked plug hanging down next to it. I couldn't find anything for it to plug into but I'd like to clean it off if it's a danger to short my electrical system(and also make sure it's not something that got disconnected) but don't know the best way to clean it. It's a 2009 Aveo5 LS with about 65k miles on it.