2004 B6 - cooling fans turning on randomly

[vtraudt]

Car parked. Locked or unlocked.
Cooling fans turn on at some time (can be few minutes, but also a long time) on their own.
I think the fan speed even fluctuates (observed ones, can't confirm all the time).

What might be causing it? Fan speed controller itself?
What module controls the fans? ECU or Convenience control module?
Possible that the ECU is bad?
Or a relay? Where is/are the relay located that turn fan on/off?

ECU is a 518AK.

VAGcom output test seems to work. No codes.

[eljay]

>> Moisture/water in the ECU compartment.

[Protection]

Yes, what eljay said. It is a pretty common issue


This was my rusted corroded relay (the relay block is directly beneath the ECU and Tcu units


The fan relay is # 219



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[ZipMeUpJ]

Ditto. Just had this issue 2 weeks ago. Had to replace the 219 and did the 373 just to be safe. That's the brake servo relay lol. Didn't want to find out the hard way if it was broken too.

[vtraudt]

Cool.
I had similar issue on C6 A6 on passenger side relay (there it was the suspension system all messed up).

Will pull relays this morning. Should be easy to spot/eliminate (likely have swap relay on hand if not special stuff).