AUX FAN NOT WORKING? Please Read this before you waist money!

[howardj10]

Just thought I would post this if it ends up helping anyone. I know the aux fans not working properly or at all is a problem for b5 S4s. I had mine go out recently and went through hell to find out it was a simple fix after spending money I shouldnt have and yes you all can laugh at me but I bet youve done it before as well at somepoint. I started by researching this on the forums and found a multitude of could be's. I started by checking all my visible dash fuses and looked for number 42 bc a tech told me that has something to do with the fans which I thought was weird because the panel said something different. I also took the battery charger and fired up the aux fans to make sure they werent the problem. I fixed the aux fan switch on the lower radiator hose with no help and finally ending with replacing the control module with no help. I was pretty damn pissed having no luck and went to my local performance shop for help and ended up printing out a aux fan circuit schematic and it said there where 2 fuses that hook into the cooling fan circuit. A number 42 thats 40amp and a number 198 that is a 5amp. The number 42 was no luck and I still think has nothing to do with the circuit and I finally got the idea that I didnt realize there where hidden fuses under the dash behind the main fuse box. I took apart the dash under the steering wheel and looked for a number 198. I saw a little fuse center up by the firewall and saw a little 5amp in the middle and assumed it was the number 198. I pulled it and saw it was not blown and was about to get in a fist fight with my steering wheel when i decided to check the rest of the fuses in this hidden spot. A 60amp fuse was to the right of the 5amp fuse and when i pulled it I saw it was blown but figured it had nothing to do with the fans since I didnt see it on the printout. I replaced it and the fans fired right up!!!!!!! RIDICULOUS! After all that?! So there it is. Make sure you check the 60amp fuse under the dash and behind the main fuse box when your aux fans stop working or your S4 starts to overheat when at idle or when the ac is on and blowing hot air when not driving in the wind. So take it from me and dont waist money on the other stuff until you check this 60amp fuse. Hope this saves someone some trouble.

B5 S4 The Car You Love To Hate

Ryan B

[hernandez3011]

Well written, I'm surprised non one answered to this thread. My fans too are not working and I have checked all fuses on the driver side panel of the dash but have not yet checked under my dash. I will do this AS SOON AS I GET HOME. I have tried everything Howard tried with no avail.

Thanks for the info

[Gaki]

well written. thanks!

[mkemk3]

How does one waist money? Jk

[Taloras]

How does one waist money? Jk

The same way one hips money, I suppose.

[zillarob]

[s4rich]

Thanks for the help,and your time.

[hernandez3011]

Well i checked the fuses under the dash panel and they're all good. Where is fuse 42 located? TIA

[00SantorinS4]

My car doesn't overheat but my A/C blows hot air (maybe I need a recharge). How can a manually check if the aux fan comes on? Simply put the temp all the way to low and I should see it kick on?

[DiscoPotato]

My fans and aux pump never turned on when I bought my car. It was a blown maxi fuse. I didn't read anything you wrote but thats just my personal experience.

Edit: just read your post that was the same fuse.

[sline22]

Here's under the dash are theses the fuses you are talking about that are mixed in with all the relays ?

[rlny]

Here's under the dash are theses the fuses you are talking about that are mixed in with all the relays ?

where exactly under the dash is this?

[DoGGRoBBer]

To the left of the steering wheel and above your foot rest.... Note picture^^^

[rlny]

is that the exact location the op is talkin about? how can you tell if those fuses are done or not

[sline22]

Under the dash above the pedals. I have a 60 amp in E slot and 50 amp in F slot. Not seeing a 40 amp anywhere.

[924Carrera]

My aux fan didn't work because the fan was dead. I replaced the fan for $250. It works now.

[sline22]

My small aux fan for AC doest work at all not after my AC went down. Had it service and still doesn't work . And the radiator secondary fan will work one day and not the next. Bad relay or sending unit possibly?

[sline22]

Just left work and when I started the car and turned the AC on both fans kicked on! WTF? What could be making it intermittent ?

Update just got home small AC aux fan not working and can't get it to engage again via Econ button. Main aux fan is working still though.

[sline22]

Tore into the car today. Both fans were bad. The control module tested fine. Took the fans apart and as I thought the brushes on the electric motors on both we shot! That's why the fans would work sometimes. Orders 2 new ones from Audi this afternoon. Will update when they are installed

[Caddy7]

Any update?

How do you go about testing the fan with jump wire? Which wire is + and -, and would I break the fan if I connect it wrong to the battery?

[Halfbreed]

I am going to check this when I get a chance. Someone wired my electrical fan (large one behind the radiator in the driver side) poorly and it almost burnt the car down. Now that I wired everything up it still won't turn on and my AC only blows when the engine is on. Could this fuse be my issue? I wired the fan to the X75 terminal, it was previously wired into a fuse in the fuse box when it went ablaze.

[Halfbreed]

Bump for help

[walky_talky20]

I would not recommend you connect a high power fan the 75X circuit. You are just assuming that circuit can take all that extra load. That 75X terminal is driven by a single relay (which happens to be high failure rate as it is). It runs the blower motor, wiper motor, rear defroster - basically all the high power accessories other than the headlamps. It is convenient to tap onto for small things, but I do not advise adding additional high-load items to that circuit.

I would recommend you use your own relay that gets power from the 30 post (or directly from the battery). You can trigger the relay however you want to make the fan behave as desired. Trigger from the 75X if you wish (not a bad idea so the fan will shut down during cranking which gives the starter more juice).

Finally, something that I find is often overlooked is that the 30 post and the 75X post are *completely UN-FUSED*. That's right. Direct 12V+ from the battery is on those 2 posts. If whatever you hook up to those posts happens to short out 5 years from now, there is no fuse that will blow. It will simply start melting down the wire harness in the dashboard. You *must* add your own fuse in-line when tapping those posts. Preferably within a few inches of the post so the chance of a short on the un-fused side is minimized.

^IMHO, 2 cents and all that.

[Halfbreed]

Walky I figured you would eventually chime in you seem to always have the answer. Well I assume If 75X is a constant 12V that my fan must be dead. When I get a new one I will be sure to wire it up the way you suggest. Thanks again.

OP, sorry for the thread jack

[ColoradoRS4]

I currently am having a fan issue too. I don't know if my fan has been working since I bought the car but I put a JHM front mount on and deleted my front electric cooling fan so now my car overheats in traffic. I replaced the sensor in the lower radiator hose and also bought a new fan because mine bit the dust and doesn't work when you apply a power source to it directly. I checked the voltage on the rear electric fan and oddly there was power at around 10.6v-9.8v. I figured my fan should turn on because there was power flowing to it but it didn't. I then checked the power on my allroad to see what the voltage should be on a good working circuit. It was the exact same. So at this point I was thinking that my new fan was bad so I plugged it in to the connection on my allroad. The fan didn't kick on right away. It took about a minute. (yes my car was at full running temp when I first plugged it in). None the less the fan was definitely working. So question is... Why is my fan not working. I checked the fuses, they were fine. So the next step is to replace the fan control module. I went to stammler Audi in boulder (the best Audi dealer to work with I've seen!) and I got the module. My next step is to install it.... Wish me luck!!!

[kbS42001]

Finally, something that I find is often overlooked is that the 30 post and the 75X post are *completely UN-FUSED*. That's right. Direct 12V+ from the battery is on those 2 posts. If whatever you hook up to those posts happens to short out 5 years from now, there is no fuse that will blow. It will simply start melting down the wire harness in the dashboard. You *must* add your own fuse in-line when tapping those posts. Preferably within a few inches of the post so the chance of a short on the un-fused side is minimized.

^IMHO, 2 cents and all that.

so would it be wise to by an inline fuse for somthing like a boost gauge?...i think my instructions had it wired via a loop to the 75x terminal....

[sline22]

I used and ohm meter and checked for continuity. Its the easiest way. And I confirmed by putting power to the fans as well. Two leads off the battery and to the connector via alligator clips.