sugaryling

Both fans behind the radiator wont come on. Even when the car is really hot (over heating) or when I turn on the AC. The AC usually triggers a fan.

I applied +12V to the fan wires and they both function. I looked for a fan fuse but I didn't find one...there isn't one right? Does this mean that my fan controller is toasted?

Where's the temp sensor that triggers the radiator fan located? Could it be a bad sensor? My temp gauge on the cluster works fine.

audiqv8

Most likely your "Radiator Fan Controller/Resistor" is shot since aux fan should start when the AC is turned on.

sugaryling

Do you know where the controller is located? How about the fan switch? I think I'll start with that first since it's about $10 sensor.

audiqv8

Search engine is your friend.

https://www.audiworld.com/forums/sho...ler%2FResistor

sugaryling

I did search and found that post too. However, that post is NOT for our C4 cars. It's referring to a C5 A6.
If I search under C4, there are no post related to "fan controller" or engine cooling fan controller."

Prospeeder

There is the thermo fan switch on the driver side bottom of the radiator. There should be a relay in the relay box for radiator fans.

dubblrest1985

around it.. I tried replacing the sensor on the bottom drivers side of the radiator. Both high and low speed works, just will not come on when the engine temp gets too hot.

sugaryling

I'll try replacing that switch since it's cheap but I have a feeling that wont solve the problem. *EDIT* Forget the thermo fan switch, that isn't the problem. The fan doesn't come on when I turn on the AC. When the AC is on the fan should come on regardless if the thermo switch is working for not.

Where's the relay box? You mean the fuse box on the driver side firewall? Which one is he relay for the fan? I've looked in the manual and there seems to be no fuse for the fan neither.

I followed the fan wires and cant seem to find a fan controller. Does this car even have one? I've tried searching Google for a fan controller, hoping to find a reasonable priced new one but nothing comes up. Makes me think this car doesn't even have one.

sugaryling

How do you test the high and low speeds? I just applied +12V to the fan wires and made sure that they are functioning.

Do you fans turn on when you turn on the AC? Mine doesn't so I think it's a bad fan controller. but where the hell is the fan controller!? I followed the wires from the fans to under the frame rail. There it connects both fans together with what Im guessing a +12V and a switch wire. So I follow what I think is the switch wire and 12+ and it disappears into the firewall.

audiqv8

Your car have a fan controller/resistor

V7 are the two fans
J26 and J135 are the relays
J135 relay is for high speed as you can see that it bypass the fan controller/resistor
S42 is a 40 amp fuse which is a rather larger fuse and will not be in the regular fuse box
N39 is the fan controller/resistor

Check fuse S42 to verify that it is good.