Ever haunted by the cooling fan ghost.
 

Some time ago on this forum I posted a question I had about my 2002 tt Quattro 225hp 6 speed overheating after a two hour drive and since then have learned that this occurred because I had "econ" active on the ac since it wasn't especially hot that day and that my cooling fan did not turn on to prevent the delayed overheat. Since then Iv'e also replaced nearly every component of the cooling system but still have only had my fans come on with the ac on.

After thorough research on topic, and posting here It was evident to me that the fan control module was the only remaining component that could be faulty so I ordered a 30 dollar replacement (mistake). After installing it neither of the fans turned on under any circumstance and the hud beeped three times and said service every time I started the car. I left a bad review for the part, ordered a decent OEM replacement from borsehung, and re-installed the old control module so that I could at least have cooling fans with ac.

Still neither of the fans came on ever / three beeps / service warning. I cleaned the 40 amp strip fuse and replaced the 30 amp blade fuses on the battery cover (didn't help), and took the car to pep boys for a diagnosis (didn't help). They said the fans tested ok but I needed a new fan control module and that they could install one for just over 300 dollars, which I declined since I can do it myself in under 5 minutes without even getting my hands dirty, with like my mini on board tool kit.

Anyway, I installed the new OEM fan control module today and still neither of the fans will turn on at all. The three beeps and service warnings are gone but still pretty frustrating. Iv'e tried giving the fans a helping push but nothing. I'm thinking the junk control module shorted something, but wouldn't that have blown one of the two cooling fan fuses on the battery cover?

I'm confused, hence this post.

If anyone wants to know how to chance the fan control module, let me know, I'm a pro now.

Failed to mention. I've also checked the mini blade fuse in the cabin fuse array. Apparently pulling it out should make both of the fans stay on, that didn't happen for me.

Damn that's a lot of debugging!

Indeed

The coolant temperature sensor is actually 2 sensors, one signal goes to the dash gauges and the other goes to the ECM. It could be the temp sensor is telling the ECM it isn't hot enough to turn on the fans while the other half of the sensor is telling the dash gauges it is hot. This doesn't seem likely but your issue is obviously a head scratcher. If you have a scan tool you can read the temperature from the ECM and see if it is in agreement with what you see on the dashboard.

Would consider the coolant temp sensor to be the issue if the fans turned on at all. When the ac is turned on both fans should turn on at low speed regardless of coolant temp. When the coolant gets hot, the coolant temp switch signals the control module to send more power to the main cooling fan. Both of my fans work but they aren't getting any power.

I feel like the cheap control module burned out one of the power wires, either from the control module to fan or battery to control module. Gotta wonder why that circuit has 3 fuses that can't prevent a wire from burning though.

I'll be taking it for diagnosis from a more reputable mechanic on Monday.