I have a 2002 A6 2.7T with 120K. The timing belt, t-stat,water pump where replaced about 20-25K ago. Work was done about one year ago by a Audi/euro shop. Okay story time. Driving home from work outside temp is -15F speed about 75mph. The big red temp warning popped up on the cluster and the temp gauge was at 1:00 (max at 2:00) normal runs at 12:00. Pulled car over opened hood checked coolant level in tank (at the min. mark) no leaks that I could see or smell. I set the Econ (a/c) to on hopping it would start one of the fans. No fans where running. I turned the heat to max and it stopped climbing. I started driving the temp dropped very slowly. It returned to normal IF I keep the heat on max.
What do I need to check?
Fans/controller
T-stat
Water pump
Thanks

 

You are going in the right direction. Since fans aren't turning on when car is overheating more than likely it's your fan or fan module that's bad. I would check power at module and fans. Or you can try to supply direct power to fans to verify if fans turn on to isolate concern. Good luck.