Larger Cooling Fan Not Running

[syd.fos123]

Hi all,
Ive recently noticed a low hum and slight vibration in my steering wheel after the engine is completely warm. When the noise occurs, the smaller cooling fan is running extremely fast while the larger fan doesnt turn at all. When the larger fan is manually moved, the smaller fan immediately slows down but then speeds up as soon as the larger fan stops. It does this with the AC both on and off, and does it intermittently while driving and idling. I havent had any overheating problems (yet and I hope it stays that way), just the vibration and fan sound. Any suggestions? I figure the fan/fan module probably needs replacing, but if anyone has fixed the same issue I'm all ears. Thanks!

 

[BRIAN427COBRA]

To see if the FCM(fan control module) is working, turn the key to the on position, don't start the car, AC on, both fans should be on, if so all is good, if both are inop, the FCM is bad, if only one is turning, replace the one that ain't working, or in your case the one making noise.

 

[syd.fos123]

To see if the FCM(fan control module) is working, turn the key to the on position, don't start the car, AC on, both fans should be on, if so all is good, if both are inop, the FCM is bad, if only one is turning, replace the one that ain't working, or in your case the one making noise.

Thank you for the response! Tried that with the engine warm and cold and neither fan turned on. However, the smaller fan does run once the engine is warm, so its only the bigger fan that seems to never work. Would it be a safe bet to just replace both fans and the FCM? And since it’s not given me any overheating problems, is it still safe to drive around? Im looking at parts, just wanting to know nothing catastrophic will happen on my commute.

 

[pedroYUL]

Is your heater core in good shape, does your front defrost work on both sides of the windshield, do you have heat on the passenger side?

Probably the big fan does need work, but it does sound weird to me that the small fan needs to work that hard in the winter.

 

[syd.fos123]

Is your heater core in good shape, does your front defrost work on both sides of the windshield, do you have heat on the passenger side?

Probably the big fan does need work, but it does sound weird to me that the small fan needs to work that hard in the winter.

Defrost works great on both sides and heat blows fine out of the passenger side as well. The smaller one is the AC condenser fan correct?

 

[pedroYUL]

Honestly, I'm not sure how are these fans controlled in the Passat NMS. I do know the mk4 platform cars have a separate fan control module, and the mk5 has the FCM integrated to the driver's side fan.

If the FCM does fail, you can have a variety of symptoms, but it could also be corroded wires. I did have "fun" chasing a fan issue in my mk4 not long ago, and it ended being an internally corroded wire.

Usually both fans rotate, either slow, fast or blast.

 

[syd.fos123]

I think I'm gonna start with the FCM since its the cheaper place to start and go from there, but will check the wires. Thanks guys for the input and help! I'll check back in once the parts come in

 

[syd.fos123]

Hey All! My dad was able to replace both fans and the FCM in a kit- $150 and 1 hour later its fixed! Thanks!

 

[BRIAN427COBRA]

I would recommend doing my little trick whenever you change the oil, that way you get blind sided again

 

[oilhammer]

The fans on that car run together, and only when refrigerant pressure is high enough or coolant temp is high enough, or during a DPF regen.

For $150 you got some awful low quality Chinacool stuff, so expect to do it again soon.