This procedure should be very similar for all vw audi make and.
Audi a4 coolant temp sensor location.
You can always detect a bad coolant temperature sensor by reading the engine diagnostic code but you can also detect it by the increase in fuel consumption the sudden change in the temperature gauge or by seeing black smoke coming out of.
How to change engine coolant temperature sensor on vw group engines vw audi seat skoda golf mk4 generation.