Thanks a lot for the specified write up. Means a lot to me.^^Good luck. I hope the by getting it to drop to a more normal height and clearing the codes will fix it.
Now, let see if we can get a basic understanding of how this system works. Here is a picture of a typical air shock. The front and the rear shocks are basically the same, the front being slightly more complicated. But they all are basically like this.
Here is the self study for the air system. http://www.volkspage.net/technik/ssp/ssp/SSP_302.PDF
Let just skip of the CDC valve. This is what adjusts you from comfort-auto-sport mode. It is not the problem and that is all we need to cover on it today.
So, now we are looking at a shock, just like any other car, with a big air bag around it. This is why there is no spring. This air bag does what the spring would do on any other car. It has the added feature that if you add more air, the car goes up. If you let out air, the car goes down.
You are too high, you have too much air in the shock. Letting the air out should be super simple, right? No, it is German. It is not simple.
Notice that there is only one air hose going in and out. The air pressure inside the shock is is controlled by how much pressure is in the hose.
But what is that thing I see? A residual pressure valve? https://aerosus.com/vw/touareg/vw-touareg-residual-pressure-holding-valve-rear.html
Now, what we usually have a problem with is leaking around the residual air valve. See this thread. http://www.clubtouareg.com/forums/f44/how-to-replace-a-residual-pressure-valve-79332.html
It is a bit of a pain to get out, and sometimes that valve strips out, as it did in that thread. It could also stick shut, which would freeze your shock in position. Now, you are thinking that is my problem. Perhaps, but perhaps not. If this was easy, we would just have you loosen this slightly to let the air out, but German cars don't work that way. lol.
You will just unhook the hose to fix it huh. Well, that will let some air out, but the residual air valve will only let small amounts of air exit the spring at one time. Hence the name residual air valve. Needless to say, this complicates everything.
Once you get the VCDS from Ross Tech, they have a forum that they will help you in. The first thing is to do a scan. You will then save that initial scan. Keep that, it will be important to have it later. Then you clear all the codes. After the codes are cleared, cross your fingers and start the car. If luck is with us, the shocks will re-adjust and this will be over. If not, we can do more troubleshooting after that point.
Oh, VCDS scans really drain your battery. Like having the headlights on type of drain your battery. Best way to do it is to have a battery charger connected to the jumper lugs under the hood. If that is not an option, a battery jump pack is good to have.
I already researched the forum, and found this residual air valve as you are speaking of. I just didnt think that might be the problem since all topics are about them was leaking around the 'air spring'.
I got hands of a vdcs today, and when i force the runner gear fault on (switching from off-road to auto ride height) the fault comes up.
02250 - Function Deactivation: Valve Duty Cycle 001 - Upper Limit Exceeded - Intermittent
Problem didnt fixed by clearing code fault
Its the rear right that is stuck.
I did as you said, left the car overnight with the air hoses disconnected from the compressor to both rear wheels.
Its funny, the rear left airsuspension blowed out tons of air, and i could see the car lowering itself.
The right rear just blew air for 10 seconds and stopped afterwards, suspension still stuck in highest position.
The car is left for the next 20 hours with the hoses to the rear disconnected, i will get back tomorrow with a check up.