Aux Fan behaving very oddly

What is going on here?

I have a 2010 S5 4.2 V8 - the aux fan runs for 20 minutes on end after shutting off the car when it’s 50 degrees farenheit out, no A/C was used, and the engine never gets hotter than 102 celcius while operating. It’s left me with a flat battery a couple of times. Now it gets interesting. When I press the unlock button on the key fob, or pop the trunk with the key fob after the car has been sitting for a half hour, - THE FAN WILL KICK ON, and run for 5 minutes!


Not totally uncommon. Check your vag com in your control modules. One of them is loosing connection. The fans actually need to be turned off all of the time by the ECU. If they loose commuication they come on.

Thank you very much; but I could use a bit more laymans terms lol.

So I need to find a local Audi club member who has a vag com cable and vcds etc and do what?

Get a vag com. Check for codes and come back. I’ll be happy to take it step by step. We would fist need to see if there are any codes.

Hey there, it’s been two months and the fan situation is only a lot worse lol it runs for two-three hours while the car is off. It’s hot out so the battery doesn’t die. However this obviously cannot go on any longer - I understand your first response better now. I feel replacing the radiator fan control module will likely fix this situation right up. I located one at a fairly local wrecker (even from a 2010 S5!) for $75. Now the question is can I put it in myself? I handled myself installing an RS honeycomb grille easily. How much further disassembly is required from there to get at that control module? Thanks so much for any insight.

A local 2010 S5 had this problem as well. The fan would stay on killing the battery. We found out that the fan and control module are one part so you have to replace both at the same time. It was like $900 something new so if you can get it for $75 then great. Basically have to remove the front bumper, unbolt the power steering/AC condensor, remove the radiator and fans as one big assembly, separate the fans from the radiator, and replace the bad fan/control module. Good luck.

Thanks so much yeah the $75 option isn’t on the table that’s not for the fan/module. Time to start calling around to wreckers…

You should be able to unplug the fan main connection on the driver side. If you really wanted to until you got money together. You could just wire up the fan to run off a switch. I did that on my S4 not because my module went bad but because I wanted to. I love switches.