Teutonix

In your case, since they're not running at all, I would try putting a jumper in place of the coolant temp switch on the radiator outlet and see if the turn. If this works, the switch is bad. If not, I'd try powering them each directly. If this works, your control unit is bad. If this doesn't work, your fans are bad.

MP4.2+6.0

What I did on my 2000 4.2. No action, thus dead fan. It had eaten the deteriorated hood latch rubber shielding that is in front of the lower hood latch as the likely causation event. Happened back in the winter when it was cool. I realized I wasn't hearing any low fan with modest HCAc setting and compressor engaged. Replaced both parts and all fine.

Teutonix

Just to close the loop on this....

I received and installed the new fan control unit (FCU - p/n 4B0-959-501-H) today, and the problem is solved.

The critical factor for diagnosis:

1) Fans were not completely in-op. They both ran on low speed, just did not kick up to high speed appropriately.

2) When A/C was turned on, the fans would sometimes pulse hi-lo-hi-lo repeatedly, but would never hold a high speed. This led me to believe the fans were physically capable of running at high speed, but they were being controlled incorrectly.

Hope this helps someone in the future.

Also note that the 3.0 (AVK) engine apparently does not have a typical radiator hose-mounted fan switch like other Audi engines. The fan speed is controlled by the ECU, apparently getting a signal from the (commonly replaced) GREEN temp sensor at the top, rear of the engine. This would be the first suspect, and I threw in a spare that I had laying around as an early diagnosis step.

gsxeclipsepsi

Hey I'm trying to track down my aux fan problem.

When my a/c turns on I got power at the connectors by power steering tank. Power in is about 10.xx This runs my a/c fan fine, I'll here it go hi and low at times.

Now I can't see to get down to the fan switch on the coolant pipe to get the connector off to bridge pins 1 and 2 for low and 2 and 3 for hi I can't reach it anywhich way when with charge/intecooler pipe removed can't get it off.

But I thought aux fan was shot, had to cut the wires to get it out cause I couldn't find its route no big deal. Wired it to battery bunch of black dirt came out and it came on.

I have checked the fuses they are ok. I checked a/c fan, the ouput at the connector by power steering is same 10.xx and it runs the fan fine. So is fan control unit shot? Or just my aux fan is shot and dont't like the signal being put out.

I live in Florida and at idle in 100*degree weather the temp gauge starts rising.

So my question is. I'm taking alt back out (advance auto 3 months ago)since it drops voltage at 4000 rpms from 14.xx to 12.3 plus and I'll have easier access to FCM if neededs to be replaced. Or do you think its that fan switch. Its really hard to get the damn clip off it.

thanks

guys

Zaphodb17

I'll bet your FCM is not bad... I had a similar problem on my 2001 A6 2.8L Quattro and it turned out to be the secondary/auxliary fan was not running properly. I replaced that with one from, I think, Pure Motorsports and THEN had to clean up the heavy guage termiminals on the Fan Control Module (there was some arcing). Now A/C works perfectly and you can hear the high and low speeds of the aux. fan whenever I turn the A/C on in hot, humid Washington, DC weather. Oh, and I had already changed the thermal fan control switch in the coolant hose on the left side of the rad (which did nada)

mschoffstall

I have a 2001 TT and i have a similar problem the radiator fans will not come on. R2 the fans, cooling fan switch in the radiator and it still doesn't work. I also jumped the wires on the switch and both fans came on. Could it be the aux cooling fan unit under the battery if so what is the trick to get the battery box out of the car do you have to take the whole front end off to get to it?

Monte

CRuby

Recently had intermittent functioning of both electric fans on our 2.7. Sometimes they run, sometimes they don't, even with 12V directly to fan wiring. Pulled fans & lots of black soot comes out. Pried back cover of fans off & can see that the 4 carbon brushes were worn down to their stop, thus intermittent brush contact. Black soot is years worth of worn carbon brushes. Choosing to replace the brushes rather than by new or used fan.

arjun90

Typically, when the passenger side fan does not turn on when the AC is switched on, the primary driver side fan will compensate and work harder.

A dud fan would leave you thinking of a problem associated with the the Fan Control Module because only one fault code would appear pertaining to the FCM (Short to Intermittent). A dead FCM would show No Signal. The short to intermittent fault code will continue show up on VCDS unless the right-side fan is replaced.

I received my fan recently; what would I need to reattach the wiring? The two wires that come off the fan were pre-spliced (barebone).

Is there a DIY? If not, how would I be able to replace the physical fan without having to go into service position?

Advice would be greatly appreciated. Thanks

02A62.7TT

Sorry for reviving an old thread but I'm having similar issues, no cooling fans working.... already tried replacing fan thermal switch and fan control unit and checked all the relays I could find and still nothing. They do run with direct power but when I jump the thermal switch I get nothing, would this point to a faulty FCU?... will a shop be able to pinpoint my issue with a scan? any suggestions would be helpful. I'm so tired of chasing this issue after I just did the whole timing chain and thermostat job, which wasn't a bad as I thought it was going to be.

georgeb944

The full version of VCDS does have an output test that includes the fan control.

A good shop will diagnose your problem and replace only the parts that are faulty, and will charge you for those parts. A shop that doesn't know what it is doing will replace parts until the problem goes away, and will charge you for all the parts it replaced.