So i recently replaced my thermostat because my car would not heat up to operating temperature, until about 40 mins of driving and anytime that i would reach a stop the gauge would go back down, after changing the thermostat, the car ran perfectly fine and the check engine light didnt pop back up. Now after about two months my check engine light came on and it takes like 20 mins to reach operating temperature but the gauge stays at operating temp once it reaches it, i changed the 2 and 4 pin coolant temperature sensor. My check engine came on again after i changed both of them and it still read p2181, idk what else it cud be unless i installed a faulty thermostat that is stuck open but then it wudnt be reaching operating temp if that was the case?

 

should we assume it is an R8?

 

Audi a4 2003 1.8l Turbo

 

I would check the basics with the help of VAG-COM:
18613/P2181/008577 - Ross-Tech Wiki
It should point you in the right direction.

Also did you clear the codes after replacing the sensors?

 

Yes i cleared all the codes and made sure everything was wired correctly