I all of the sudden got a rock hard suspension on my W211 E55 and since it happened on atleast both rear sides at the same time I think it is highly unlikely it's a case of the shocks being ""worn out", I'm leaning more towards either an ADS control or wiring failure.

I checked the resistance for the solenoids in the dampers and they are all in the 11.9 - 12.4 ohm range.
When i drive and get to about 20km/h the system goes active and sends a voltage to the solenoids, in comfort both are active, in sport I and II, only one depending on mode selected so it seems ok.

What I'm not sure about and want to ask about is if 5.5 Vdc is correct or it it supposed to be 12Vdc?

I'm thinking there might be something wrong in the control unit that causes a voltage drop and this lower voltage isn't enough to actuate the solenoid valves to their fully open position.

 

Oh snap!

I don't know why I never thought of hacking the Airmatic to be even firmer, I just threw it out immediately.
Inline Airmatic resistance/voltage modification could in fact be a way for people to get a sportier ride without having to commit to coilovers.

Not what you were interested in hearing, but an interesting thought.
My car has Airmatisectomy done to it, otherwise I'd go measure for you.

 

I think 5 volts is correct. I saw a thread about this somewhere and they did eventually figure it out. If you can't find it here, try a site wide search. It might have been an ML suv. Sorry, that's not really much help.