aTOMic

I had a front strut leak and sometimes the whole car WOULD go flat overnight. My understanding is that there is only one pressure sensor for all 4 airsprings and the tank, so there is probably either a mechanical valve arrangement in the distribution block or an electronic arrangement to sequentially read each (or most likely a combination of both).
As for why both fronts come down, I recently discovered in VCDS grp 34 Adv measuring Blocks the "axle airspring lock status - on/off" (or something like that) ; I think the suspension monitors and adjusts in case of one sided air leak which would cause an unstable condition and keeps the axle (i.e., the front or rear) level. This would explain why always the front or rear sags and not just the one defective shock... Just my theory, undocumented as yet.

At one time I had a pump go bad and while diagnosing it over several weeks, sometimes the front would be flat in the morning, sometimes rear, sometimes both. I chalked that phenomenon up th the valve block's "rotating" valving for the pressure sensor.

-Tom

iloveandhateaudis

Read through all of this, informative. My car lowered front and rear this past November (2016) at first cold spell. New compressor at shop. $$$$$ Decided in order to keep this particular A8, (my 3rd....love them...and hate them...or should I say, hate my lack of knowledge about them) I needed to get educated, so I came here. Onward....Car lowered again day 2 of having it back, then went back up. Has intermittently gone down, but not as far as it did day 2, and lately as in the past several weeks, it will lower a 1 to 1.5 inches in the fronts. Its been warming up here...which I think affects how quickly the car lowers (seemed quicker in the single digits of January), but it is so wierd and random too. It seemed to be the rears would lower the same but not lately at all. I've been measuring from the rim to the fender ..when at 'comfort' setting and green light goes off, it sits 5" from top of stock 20" rims to fender in the rears, 5.75" in front. I cant tell if one side is lowering before the other in the front, at least I havent noticed that, been checking every few hours at times. SO, from what I've read here, this points to strut replacement right? Some have said using spray bottle test wont be effective to diagnose? Oh...one other thing, the car will not active jack mode. I click on it, it just flips itself right back to off mode??

MP4.2+6.0

Yes, in general pointers are to a bad strut. One of the two fronts given front drop. And unfortunately prior compressor replacement was likely a symptom due to overwork, not the true cause. Same worm is eating away at the new one. Given how much your compressor has been (over) working, as a slight aside I would also replace the compressor relay if it was not done as part of recent compressor replacement. Audi recommends same in a service bulletin. If relay fries closed, it will burn out yet another compressor if you don't literally pull the power before it craps out.

To get to your observations and questions, some have reported issues with cold and increased dropping problems, but assuming it may be true, it would also depend on exactly where the leak is and how temp. differences affect the exact area. Yes, some have had success soapy spray water testing a strut. Others--including me--have found absolutely nothing. Again, depends on where leak is most likely. Some have also been able to hear it, but probably more when it is pronounced. Mine took a day + to drop fully, and even in a quiet closed garage where I parked it, I heard zero.

For me I finally had to rely on just visual dropping observations, plus eliminating other possibles. I got about 90% comfortable which corner it was by watching it go down--definitely in front. I found the bad side would bottom somewhat before the other side; I wasn't as sure while it was in the process of dropping over the day or so it took, but when I thought I saw a difference toward bottom it was always the same side (passenger front). You definitely want to be on flat ground watching it--no meaningful slopes in any direction. The differences from side to side when observed are subtle--under an inch IIRC. To be thorough and since strut work is more involved and $$$, you may also want to eliminate the (air) valve block. If it leaks at one of the strut air outputs contained in the the overall valve block, likely similar visual result. You can definitely soap test that. On a W12 like we both share experience wise, it is behind (USA) driver's side plastic fender liner, on the "back side" toward the passenger compartment. Once I sprayed mine thoroughly and still found nothing, I ordered up the right front strut. Problem 100% solved, immediately.

iloveandhateaudis

THANKS! #1. Just ordered the relay from Partsgeek. Found this video for that: #2. Will watch carefully to see if I can clue in as to which side is bad like you did, hopefully not both. Not sure if this can be related, but I also have bad upper control arm bushings and/or sway bar links (that I believe you also helped point out in another post, my first here) in the driver front side...soooooo, is it possible the strut is more likely than not to be bad on the side where other suspension components are failing/have failed like these bushings/sway bar link?? #3. Is there a video anywhere of how to get to the valve block to test? I couldnt find one searching.

MP4.2+6.0

2. Not likely the suspension parts are related to the air leak. The correlator is miles and age, not proximity. If you have to pull a strut BTW, essentially no incremental mechanical work to do upper arms if worn and on side you haven't already done.

3. No known video. The work is basically pulling driver's fender liner to get in there. From memory:Push pins are about the size of a quarter face on. Some old ones have a plastic screw in center instead of a round pin, but same function. Buy new ones from dealer in advance; typically get trashed if you try to pry out and re use.

After that you will see valve block right there in back of liner area. Simple mechanical stuff to loosen it up from bracket support so you can inspect and spray w/ soapy water bottle. Don't disconnect any air lines.

Same fender liner removal BTW --or at least pulling front away--is also needed to get at a plastic clamp below driver's side W12 air box, which also comes out to check power steering fluid buried down there. Or, to go in front of fender liner area on that side to change the HID bulbs if desired/as they get old. Fender liner also comes out to undo upper control arms if whole strut unit isn't pulled. In other words, std. D3 operation for a variety of things, esp. W12. Once you have it out once, you will understand much better "how the hell" you can indeed actually get in there on the sides to do whatever required work with such a wide motor. Those push pins, some similar hidden door card plastic pins, and an inexpensive intake manifold riser gasket were my various on hand small parts for W12, plus what ever for a soon to come tune up, brake work, etc. The intake manifold is similarly hidden obstacle in plain sight that if (surprisingly easily) removed allows you to get under it as well as just barely in back of upper motor area for other work.

progolfer9

Hi everyone...
I need some advise / help / suggestions. I have been noticing a funny situation with my A7 lately.My car comes with audi drive select and aslo with air spring suspension. I notice that the rear right tyre air suspension sinks (touching tyres) after about 1 hour after parked. All other suspensions are at normal position no sinking noted. The A7 has a raise/lower function , with the suspension raised position and the the suspension didnt sink at all for the rear right tyre.

What would be causing the sinking when its on normal lower/standard mode.
Looking forward for some replies. Cheers and thanks

Jack88

You have a leaky strut or valve block. Easy.

WScott8

I don't know if you guys are familiar with this supplier, but I discovered them a few days ago... Hope this helps any and all affected by the air ride issues, I'm a victim as well...

https://aerosus.com/audi/a8-d3.html

MP4.2+6.0

+1. And, fix before it burns up compressor or cost of repair can approach double.

iloveandhateaudis

Finally got to this. Jacked car with stands in front, pulled fender liner, valve block right there driver side as u noted. Sprayed...bubbled in 2 lines badly, one a little. All corroded badly. Jacked car up in back, unplugged valve block, and then removed all air lines from block, then removed all corrosion with a brush and went to Ace Hardware and purchased .25 cent rubber seals and one .25 brass sleeve to replace a sleeve that was broken removing lines. Greased the connections up to repel water and maybe prevent future corrosion a bit, and put everything back together, tightly, put block back in, wheels back on (did the upper control arms/sway bar link in the middle of this), turned on, aired up, and has stayed up. Think I got lucky fixing this for $2.00 in parts.