Fans not working - STUMPED!?

[Wheelbarrow]

2004 Audi A4 3.0

Backstory - My fans used to come on and were probably on high the whole time. When I would turn the car off they would sound like a jet engine spooling down. At the time I had no idea that it was a sign of troubles ahead. Now the fans don't come on at all. Here's what I've done:
*Replaced the Coolant Temp Sensor
*Replaced the Fan Control Module
*Checked that the fans were ok by jumping 12v to them. Both came on fine.
*Checked the relay (219). Put power to it and verified that it had continuity. Checked out fine.

After all this the fans still don't come on. With the A/C on LO (full blast) the smaller fan kind of twitches like it's trying to come on but doesn't quite make it. The other fans does nothing at all at temp.

One thing that I haven't been successful at locating is a fan temp switch which is supposed to be located on the lower radiator hose. I can't seem to locate it on my vehicle. There's a plastic housing that looks like it has a place for a sensor but it's blocked off. And it looks like it came from the factory that way. When I purchased the Coolant Temp Sensor from the dealership, they had a hard time determining whether my vehicle had one or not, even when looking it up using the VIN.

Also, the fan control module I bought was a super cheap one. It may very well be that I got a piece of junk, but before I spend the money and time on replacing it, I want to be sure that I've exhausted all other possibilities.

So, are all 3.0's equipped with a Fan Temp Switch (or similar name) and if not, what sensor tells my cooling fan (not A/C) to come on?

Thanks in advance!

[pablolizarraga]

My car (3.0 BGN) is same as yours. Bottom radiator hose looks like sensor should be there but it's blocked of and it looks OEM.

I'm adding diagram and subscribing to this thread because I'll be addressing the FCM if replacing my nonfunctional accessory fan doesn't clear FCM fault code. Whatever is recommended for your issue may help mine. Good luck.



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[Wheelbarrow]

Yes, that's exactly what I was talking about. It looks just like that except there's no sensor. Thanks for the diagram. I did some more testing with the voltmeter over the weekend. I have to do some more tonight and I'll post the results when I'm confident that what I'm seeing isn't just a fluke. I'll try to be very descriptive in an effort to help you solve your problem as well.

[Wheelbarrow]

So I'm resurrecting this old thread in the hopes it will help someone else who is having the same issue with their fans not coming on. Yes, it took me nearly two years of casual searching (granted I didn't have to really worry about overheating in the winter) to find the solution. After trying all of the things mentioned in the first post, I finally found the problem (I should add to that list--replaced fans, and replaced FCM--again). It was the 60 amp fuse that is under the dashboard. You have to remove the bottom cover of the dash in order to get to it. That fuse had melted to the point that the contacts sheared off in the connector. I found another connector at the local junkyard (with a good fuse still in it ), cut out the old one, spliced it up and the fans work great!

[pablolizarraga]

Glad you sorted it out. I was on the same casual timeline as you because I finally replaced the accessory fan a couple of months ago; no more FCM fault codes.


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[CarsnPlanes]

Resurrecting this thread. If anyone reading this knows where the coolant temp sensor is on a 2004 A4 3.0(AVK engine). I read that it doesn't have the separate temp switch shown in the illustration above from Pablo. I checked under the car on both sides of the radiator and nothing. Read that this engine/car combo has a dual engine temp switch which I assume one set of wires would serve the cluster temp gage, and the other would serve or trigger the need for the radiator cooling fan. I don't know if all the wires would first go to the ECU for the ECU to control the temp gage and fan control. I have a situation where the fans come on even with key off and so just trying to find out where the fans get their signal to turn on.