Hello, I recently acquired a 2000 Audi TT through an inheritance and have found your site very helpful as this is my first foreign car. Ive had the car for about a month now and on and off the car is getting close to over heating judging by the temp guage. I have discovered when the car is getting to this point, neither fan is running. HOWEVER when I turn the AC on, both fans are coming on and the car cools down.

Any suggestions on where to start?

 

So the cooling fans will not come on no matter how hot the car/engine get yet turning the AC on turns both fans on? Just trying to make sure I understand you correctly.

 

I would take the chances of replacing the auxillary fan switch

 

you are correct, no matter how hot the engine/temp guage gets, the fans will not come on unless I turn the A/C on.

 

^Right on. Cheap place to start in diagnosing the problem. If you're good with a multimeter you could verify that the signal is being sent once the coolant temperature sensor reaches it's "target" temperature.

 

ok, its worth a shot, now you are saying to start with changing the auxilary fan switch not the coolant temperature sensor right? These are two different parts I suspect.

 

In looking this up for you I found 2 choices on that fan switch. One is p/n 1J0-959-481-A for 32.18 and the other is 1H0-959-481-B for 33.12, both listed the same temp range and that they are 3 wire units. You'll have to get the part number off your old one so you get the exact one you need. I did find a fan control unit also, it's a year 2000 split and runs you 126.48 or 148.80 depending on which you need per vin #. I wouldn't think you need that since the fans come on when the ac system needs them to. I suppose it's possible that the ac signal is fed into the control unit through a different channel and the fans come on for you, but that the temp sensor in the radiator could be working and sending a signal that the cpu doesn't see so the fans don't come on with that signal.

On older VW's I had which had 3 wire sensors, when bypassing the switch to test the fans and relays I would get a low speed fan and a high speed fan speed. If I got both those then I knew the fan switch was bad. You could test your switch this way too.

I was trying to find a dual fan relay, or any fan relay but only found that fan control unit I mentioned above. I'm hoping I'm wrong but I don't believe your car has fan relays. I did find a few of the basic 4 pin relays used on the relay board but no identification as to the system they are for. You should check a repair book, owners manual or if you have a relay board cover with descriptions on it that might answer if or where the fan relays are on your car. If in fact it is the basic 4 pin relay those are inexpensive and you can get them almost anywhere.

I hope this helps. Thanks, Jeff.