I have a 2004 Audi A6 2.7t with about 35k miles. Radiator fan is running for 10 - 20 minutes even when the engine is cold, for example, afterturning the car on for 30 seconds Dealer did not show any diagnostic faults and recommended
replacing the temperature sensor, Had the local shop replace the sensor(dealer wanted over $300) but the situation remains.

So the questions is: what to check or replace next?

Thanks for the help.

 

Which fan? The one on the engine side of the radiator or the bumper side of the radiator. If its the one on the bumper side then theres something wrong with your main fan. That fan should only come on when the main fan fails or the car begins to overheat. If its the fan on the engine side coming on and the ac control head is recieving the proper temperature signal, then youll probably need a fan control module. It could also be a bad ac control head.

 

It is the bumper side fan, that was remaining on. For the past five days, the problem has not recurred so I'm just monitoring it at the moment.

When you say there "might be something wrong with the main fan", were you pointing to any specifically? FYI, the car has not been overheating and the temperature gauge seems to report temperature in the expected range.