I took my Allroad out this morning in 6" of snow, -3C, and she behaved perfectly. The suspension sat at level 2, the ESP turned off when I pressed the switch etc. It was just like Audi had intended: safe and fun
I then parked up, with suspension on standard level 2, and left the car for the day.
When I got in this evening I realised almost immediately that the suspension was right down, even below level 1. The one solitary level light (for position 1) blinked constantly, and neither of the adjuster switches would 'lock on'. I couldn't turn the ESP off either.
I drove like this for 20-30 minutes, got out for 5-10 minutes, then restarted the car. For a few seconds, standing outside, I could hear a sort of "clattering" noise coming from near the back end. I've not noticed it before, but then I don't generally stand there looking to see if the car will rise up like an elderly Citroen DS either! It didn't rise so after a minute or so I got back in, and drove for another 20-30 minutes with the position 1 LED still flashing constantly, the adjuster switches unable to do anything, and the ESP still stubbornly refusing to deactivate.
I then stopped to buy diesel and, as I restarted the engine after that and drove off, resigned to more suspension-less banging and bouncing for the rest of my journey, so the car climbed back up to level 1 all by itself. The ESP deactivated when I pressed that button too. Then with a couple more presses of the 'up' button we went through level 2 to level 3. The car is now sat happily at level 4, in my drive.
I'm confident it's not a sensor fault because last time that happened the Xenon headlight self-levelling warning light came on, and stayed on for about a month until I fixed the sensor! I'm also confident it's not a punctured airbag because I have no warning light in the speedo to indicate the compressor working overtime, and if that was the cause it wouldn't have risen up after an hour and be sat tall now.
So I'm guessing it's something electro-pneumatic.
My first though had been that the compressor was frozen and couldn't pump up. But that wouldn't explain how the suspension came to be down in the first place...
While parked during the day I had unloaded a few bits from the car and occasionally when I have done this I have heard a 'hiss' from somewhere underneath, presumably as the car self-levels to compensate for the changing load or something.
So could this be what happened today? Except that this time the air dump valve (if there is one) got stuck open and couldn't close, possibly because of moisture in the sub-zero air icing it up? And being stuck open it simply drained the suspension of air, and rendered the compressor unable to refill it?
Has anybody experienced anything similar before?
Is this even how the suspension works, or have I surmised incorrectly? If I'm right, where are the dump valves, and what (if anything) can I do to stop them icing up again?
Finally, I have 200 mile round trip journey ahead of me tomorrow, so (increased risk of crashing aside...) is it bad for the car to drive with the suspension bottomed out like this if it 'collapses' or 'gets stuck down' again?
Any and all thoughts and advice greatly appreciated.