Ive been wrenching on my own cars for over a decade now and Ive handled my fair share of Audi maintenance on my 2016 C7 A6 but this air suspension issue is really starting to get to me. Usually I can track down a leak pretty fast with some soapy water but this one is being stubborn. The front driver side keeps dropping overnight and even though I swapped out the level sensor last month thinking it was just a calibration glitch the problem came back.
I hooked it up to VCDS and Im seeing some codes for the compressor duty cycle being too high so I know its working overtime to keep up. Im trying to figure out if its the actual bag itself or maybe something in the valve block acting up because I really dont want to drop 800 bucks on a new strut if I dont have to especially since Im supposed to drive down to my cousins wedding in Philly next week and I need the car reliable. I already checked the lines for kinks and did the spray test on the visible parts of the strut but nothing.
Is there a specific sequence I should follow to isolate the leak without just throwing parts at it? Like should I bypass the valve block first or check the reservoir tank connections before I tear the whole front end apart? Just trying to map out the teardown steps before I spend my whole Saturday under the wheel well...
Regarding what #1 said about "In my experience, if one side drops, it..." being the bag, they're spot on. But dont go dropping 800 bucks yet. I'm really satisfied with just swapping the spring with the Miessler Automotive Front Air Spring Bellows. It works well and is way more budget friendly for your trip. TL;DR: Replace the bag, not the whole strut, to save cash.
In my experience, if one side drops, it is almost definitely the bag itself. I fought this same battle on my A6 for weeks before I realized the leak was hidden in the bellows fold. Picking up the Arnott New Front Air Strut AS-2814 saved me a ton compared to OEM.