A8Pete

I have a 2004 A8 4.0 Quattro. I have noticed recently that the engine fan seems to be on rather a lot. It seems to come on almost as soon as I start the car and then stays on. Is this normal? If not what should I look out for?

Many thanks

03_AR_CO

coolant temperature sensor, impossible to say for certain without a scan however.

mishar

It is not only engine fan. It is also air conditioning fan. Try turning it off and watch for the fan.

A8Pete

Ah, I hadnt thought about the aircone fan. I'll try that first. If not, what module on the VIAG should I be looking for error codes etc?

MP4.2+6.0

Testing wise, turn off A/C during a cold start. If fan kicks on right away even from cold you have an obvious issue. If car is in proper shape, you should have no fan at cold start with no A/C and slow/quiet fan at cold start with A/C. And, if it's the jet engine high speed fan loud whoosh sound at start up--the one that often catches people's attention--you have a definite issue.

It can be the temp. switch as others have said--a cheap part but can be kind of buried to get at (and quite hard on a W12). But it can also be one of the fans. Not sure about reading codes, since I diagnosed a similar issue on my 2000 4.2 "the old fashioned way." Eventually I traced it to the main (variable speed) electric fan eating a piece of rubber trim Audi put behind the hood latch for air deflection purposes that rotted away. Fell into the fan and apparently locked it up at some point. Had the jet engine whoosh sound--that car had two electric and one belt/clutch fans. If I remember right, in that case the main fan was essentially disabled so the noise was not from cold start up. But once it heated up and the clutch fan couldn't handle it, the jet whoosh booster fan cut in way more than normal to deal with it. Changed out the pancake fan unit for the main electric fan and all immediately back to normal. The D3 set up is a bit different fan wise and packaging varies some with motors, but the principles are the same--variable speed capabilities, multiple fans to sort out, the helper fan function, etc.

A8Pete

Thanks guys. I'll hook up the VIAG and check through the various modules to see if I can find an error code.

Some time when I switch the ignition on the fan starts (loud jet type roar). If I turn the AC off it doesnt go away. When I start the engine if it hasnt come on at ignition it then starts with the engine so something isnt right.

I'll start with the coolant temp sensor. Can anyone tell me where it is, so I can go and take it off. Many thanks.

mishar

Check this tread.

A8Pete

Thanks Mishar - I best get the VCDS connected and check errors. The VCDS thing is still new to me. Where do I check for errors. Do I need to go to the specific module or is there a general code repository. If its a module, which one is it?