OK , I have a 2005 w220 s320cdi, I have the common Airmatic .. visit workshop problem... EXCEPT I dont!
The airmatic works fine, the raise car works fine, the different suspension settings work fine, then suddenly the airmatic stops working, pump not cutting in, car doesnt sink so continue driving , carefully. The next day car is started and airmatic fine and so on for a few weeks then is stops again , and so forth. Took to my mechanic the other day as it had been showing fault for a day and half, by the time he started it to sort the problem .. it was working! I have changed the relay to a Hella, and on one occassion I did drop the cover at the front and check the voltage to the pump and 0V ! Thought the control line may have been damaged as it was bent very tightly thro more than 90 deg and cut and resoldered extra cable in place. When I reconnected the 2 plugs pump started working and all was well for a couple of months.
So what , other than the relay , can stop the pump being supplied with the necessary power! Obviously the fuse isnt faulty or it would never work!
Any Ideas greatfully received