B9 S4 - Car making a loud humming noise…

[Ana318]

Hi there, I have a 2018 S4 B9, owned it 2 years at the end of this month. No issues, other than a faulty wing mirror heater, done under warranty last November. I do a lot of miles at the moment commuting, upon average 100 per day. Today, from a cold start (in inclement weather) I drove 25 miles - not hard miles, just a sedate drive in D mode. After 20 miles I realised that the stop/start system wasn’t working and there appeared to be a very loud hum coming from the engine. However, there was an artic in front of me and I thought it might be that. When the artic turned off and the hum continued I pulled over and manually disengaged the ignition. Usually when I do this, the car stops and all noises (apart from quite a quiet fan) cease. Today the car continued humming and slowly wound itself down, it sounded a bit like a jet engine or a helicopter. The noise didn’t happen again on that journey, but the start/stop still wouldn’t engage - FYI the ac wasn’t running particularly fast, cold or hot, it was on number 2 fan @ 19 degrees. I went about my business for about an hour, returned to the car, no noise and s/s system operational once again. Drove another 25 miles without issue. Called Audi and booked it in to be looked at, but they have no availability until the 15th. I wasn’t too fussed as it seemed to have stopped anyway. However, this evening I popped out for a relatively short journey of 8 miles and it happened again. Temperature is fine, not any different to usual.

Any ideas?

I filmed it for the audio, here is a link to youtube -

 

[Ana318]

.

 

[hellodave]

If it's the TFSI it'll probably be a failed thermostat. Almost a standard fault on this engine - search the forum for more info

 

[Ana318]

If it's the TFSI it'll probably be a failed thermostat. Almost a standard fault on this engine - search the forum for more info

Thanks, that’s really helpful.

 

[Ana318]

Hi again, this light has just appeared- is this still consistent with thermostat issues? Book is saying emissions system

 

[eggraces]

Hi again, this light has just appeared- is this still consistent with thermostat issues? Book is saying emissions system

That's just the standard "check engine" light, could be anything. Car you get hold of a code reader? Failing that any local garage will be able to pull the codes for you for a few quid, only takes 5 mins

 

[hellodave]

Hi again, this light has just appeared- is this still consistent with thermostat issues? Book is saying emissions system

Yes, that's the next stage after fan noise.

I say this as an S4 owner on his third thermostat

If you have Audi assist it's worth calling them - may allow you to get the car booked in earlier.

 

[cuke2u]

Here is the thread https://www.audi-sport.net/xf/threads/start-stop-system-fault.350876/

 

[Ana318]

Audi Assist (AA) chap came out. No fault registered and car not symptomatic. He refused to recover it, despite my video/photograph of faults. Told me to go back to Audi dealer

 

[Ana318]

Here is the thread https://www.audi-sport.net/xf/threads/start-stop-system-fault.350876/

Thanks buddy!

 

[Ana318]

Yes, that's the next stage after fan noise.

I say this as an S4 owner on his third thermostat

If you have Audi assist it's worth calling them - may allow you to get the car booked in earlier.

Flipping heck. My Manufacturers warranty is up in 3 weeks. Yikes

 

[cgomes00]

Hi there, I have a 2018 S4 B9, owned it 2 years at the end of this month. No issues, other than a faulty wing mirror heater, done under warranty last November. I do a lot of miles at the moment commuting, upon average 100 per day. Today, from a cold start (in inclement weather) I drove 25 miles - not hard miles, just a sedate drive in D mode. After 20 miles I realised that the stop/start system wasn’t working and there appeared to be a very loud hum coming from the engine. However, there was an artic in front of me and I thought it might be that. When the artic turned off and the hum continued I pulled over and manually disengaged the ignition. Usually when I do this, the car stops and all noises (apart from quite a quiet fan) cease. Today the car continued humming and slowly wound itself down, it sounded a bit like a jet engine or a helicopter. The noise didn’t happen again on that journey, but the start/stop still wouldn’t engage - FYI the ac wasn’t running particularly fast, cold or hot, it was on number 2 fan @ 19 degrees. I went about my business for about an hour, returned to the car, no noise and s/s system operational once again. Drove another 25 miles without issue. Called Audi and booked it in to be looked at, but they have no availability until the 15th. I wasn’t too fussed as it seemed to have stopped anyway. However, this evening I popped out for a relatively short journey of 8 miles and it happened again. Temperature is fine, not any different to usual.

Any ideas?

I filmed it for the audio, here is a link to youtube -

Did you manage to resolve this issue properly? My 2017 S4 B9 Avant is having the same issue right now.

The garage (not Audi) have installed a new thermostat but I'm still getting the red warning light.
It says "Coolant temperature: too high. Let engine run with vehicle stationary".
I'm wondering if there are any other sensors that needed replacing in addition?
My coolant temperature doesn't seem too high, but I can't be 100% sure.

Also what causes the fan to make that unique humming noise? Mine is exactly like your video.
It's audible from inside the car whilst driving for me as well.
Is the motor on the fan on its last legs as I've not heard the fan make that noise ever before.
I'm used to the fan running for a certain amount of time when the engine stops, but I always believed that was to cool the turbo.
Is it possible the water pump is affected as well?

Any helpful comments or advice would be greatly appreciated.