For the past two months, my A4 has been doing something really weird when it gets below 25-degrees outside.

When it's below 25, my power steering makes this loud vibrational tone (the steering wheel itself doesn't vibrate though)... It sounds somewhat like blowing on an empty glass bottle head... that weird tone that emits from the bottle -- but imagine that for my steering wheel.

If I drive straight and don't turn it, it's perfectly quiet and rides fine... it only happens when its cold and while I'm turning... but it's LOUD.. and I'm afraif something's grinding.

I did the obvious thing I knew to do -- check the power steering fluid... And the first time I did this, it stopped... BUT... the next time it got cold, it started doing it again, and when I checked the PS fluid, it was full... so I'm really puzzled by this...

I'm taking it to the dealership this week, but I want to have SOME concept of what this might be before I let them quote me a price to fix it.

Any suggestions or possibilities you can share would be greatly appreciated. Thank you!!

 

What you are experiencing is cavitation in the line. This was described pretty well here:
https://www.audiforums.com/forum/sho...ing+cavitation

Basically you have air in the system. I am dealing with the same issue. Mine started in the summer and the fluid was low. I added some, and it went away. Now it is back (its -15). When I check the reservoir I see froth, which means air is being taken in to the system and that air moves through the pump and that is the whining noise you hear.

The dealer will surely screw you. MSRP on the pump is near $500 and they will charge you an arm and a leg to fix.

I found some discount sites for a pump, but at this point it is too cold to work on. I also am trying to 100% diagnose the pump, and not a cracked hose or something, but I, like you, see no obvious leak so that points more to the pump. I surmise that the cold weather causes seals to shrink/crack and this allows air into the system causing the cavitation.

I am curious as to what you find out, as I am in the middle of diagnosing the same problem.

It should be noted that you will not end up stranded anywhere if the p/s goes out, it will just be harder to turn the car.

 

The dealership replaced two hoses that were damaged/cracked? attached to the power steering pump. I haven't gone to pick it up yet, but they assure me it's fixed. They charged $400, which included $70 diagnostic charge, flushing the power steering fluid out and replacing it, two hoses and labor. The service rep told me what you already said -- cavitation -- air was being sucked in... and there were bubbles floating in the fluid when he removed the cap.

 

Only use 11S power steering fluid.

 

11S fluid? Huh? I just use the Audi fluid Pentosin..

Anyway, glad you got it fixed. I may try to replace the hoses first on my ride... But of course I will have to wait until it get warmer near me (Michigan), its like -12 right now !

 

Audi Pentosin is good.

 

What hoses did they replace? I looked at the parts.com site and they show 3 hoses?
High Pressure, Return and a Suction hose? Anyone care to elaborate on these?

 

good luck