P2181 Cooling System Performance
 

Hey there newbie here.

My 2013 B8.5 A5 drives great but I got a check engine light the other day and the error code was "P2181 Cooling System Performance." Researching this tells me it can be one of a few things: Bad temperature sensor, thermostat, or water pump.
Well, the temperature gauge in the car works fine. In fact, it gets up to its normal operating temperature just fine. The only indication that there is an issue is the cooling fan is at max speed even when the engine is cold and of course that check engine light.
Any ideas on what the deal is?