adamsrotors

2013 L has 52k miles on it and oddly enough on a long drive to Napa yesterday, got a suspension fault randomly.
nothing seemed wrong and assumed it had something to do with the full car (4 people) and my lowering link dropped car...arrived and returned home without issue.

on the way home it popped on again. it resets every start-up, but today, it's gotten noticeably worst.
the fault comes back after 15+ minutes and now, after leaving the car up in "comfort" while off and parked, come out to the car after an hour and it's down, empty.

any tips on how to diagnose and how difficult is this fix?
are there any common issues w/like the valves/manifold, tubing/airline, or fittings?
any DIY's or threads anyone can link? did a 4 page search and found nothing specific to the D4.

thanks!

FA8L

I don’t have a lot of experience with OEM air but years of aftermarket systems. First thing I’d check if you can get access to it is any leaks or small splits/cracks in the air spring, leader lines n air lines or fittings. I doubt you’d just randomly sprung a leak in the manifold. Get like a spray bottle of soapy water and spray any lines or fittings or air spring and see if there’s any leaks that way. I haven’t been under the car yet and don’t know what anything is but just a few tips.

Forcefed4door

52k miles and lowering your car will further diminish life expectancy of your suspension. Ide see which corner seems to be lowest after air loss and figure that's the bad strut. If all corners are dropping equally you most likely have a leaking air line which will take some time to pinpoint with soap water.

FA8L

Yeah that’s right that’ll take forever with soapy water. For whatever reason I had thought you already pinpointed which corner it was.

Forcefed4door

Just seen he said front corner in his title haha. So most likely if it not any visible air line at that strut, it's the strut. Probably a pricey sob too

adamsrotors

thanks for the tips FA8L...I know these well having build many bagged cars.
was looking for anyone with D4 leak experience specifically, hoping maybe there is a common weak point or a go-to location to look for, etc.

and Forced, thanks for the lower shaming...that's so audiworld-like.
it's really not, as it's done with lowering legs, on the stock system; the car only sits 1" lower than stock, running on less air...it's infact NOT at all more strenuous whatsoever.
this is the safest and most ideal way to lower a factory system and was done within safe parameters. the only issue is more strain on the stock compressor if adjusting heigh more often, and even then it's moot.
we have lowered (and raised) many OE air suspension vehicles (Audi, Land Rover, etc.) without issue. these things happen to all cars. was just coming for some direct advice!

Forcefed4door

Wasn't knocking the fact that you lowered it. Just the fact you stated having a problem like this with only 52k miles. As we all know once you start modifying, crap is gonna happen at "only 52k miles"

FA8L

Yeah I get you. Unfortunately these systems seem much more complicated than they need to be and I’ve got zero guidance. Only other thing I could recommend is potentially hit the D3 board since the systems between these platforms are very similar.

adamsrotors

car came from the east coast...I'm assuming weather/temp swings and such played a factor, tho the car shows no other signs.

MP4.2+6.0

Using D3 experience, leak is usually in a strut. Probably 80-90 percent of time. Occasionally it is the air block (the valve control). In turn most leaks are also a front strut, with small percentage in rears.D3 and D4 are pretty much same set up, other than compressor and I think valve block moved from driver's fender area on D3 back to underneath rear around spare tire area for D4.

You can try soaping, but it only works for some leaks/depends on exactly where leak is.

Normal test is to park car on level ground. Put it in jack mode, which prevents compressor from trying to pump it back up if leaking--even with key off since it tries to self trim; jack mode kills that. Watch it in following hours or day. Assuming front, it will go down while back stays up. The problem is both sides drop pretty similarly due to weight transfer as it drops and forced over the sway bar linking two sides. So, you have to watch carefully for which side seems to go down more and a little faster. It may be only about ½" delta from side to side, so watch carefully and maybe check w/ tape measure as it falls. Once you conclude which one it seems to be, try soaping it to confirm a leak. But again it may or may not show. Sometimes you can hear the air pissing out too, but you need a quiet inside garage for that, and leak has to be pretty substantial. To really nail it, you also soap test the valve block, typically to exclude that as the leak source. At least on D3, you can soap 100% of it, so leak test there is pretty definitive. But most of time it is the strut, especially if you pin leak and related drop down to a single corner.

Assuming it is a strut, you choices will be either $$$$ via dealer (over a grand each), or rebuilts in maybe $5-700 range. On D3's rebuilts probably have a 20-50% failure rate from the endless posts about them. They may have a "lifetime" guaranty, but by about the third failure (sometimes leaks, sometimes rattles), that gets pretty old even if part is "free". Those who go rebuilt with more experience and patience sometimes try to get their own rebuilt instead of taking some random trashed core that gets reworked. Rebuilt by the way may only be a glorified paint job and o ring kit given folks experience with follow up leaks, rattles and other things, so definitely a mixed bag there that doesn't make cost savings tradeoff so black and white.

Finally, one more sometimes overlooked, well duh: Scan it with VCDS. On D3's you typically don't get more than a general leak code, but sometimes you get something specific to a corner, a sensor, compressor, etc. Get to bottom of it quickly too. A good percentage of time on D3's owners let it slide, strut is leaking and then compressor gets overworked and burns out, leaving another big hole in wallet and more repair time for now two pricy parts.