2003 x5 suspension problem (cannot find answer)

[dvc]

Hope someone can help
I have the dreaded "self level inactive" on my dash. It has been on for a few weeks and I have tried to diagnose it.
My x5 sits very high in the rear, and the ride is very stiff.

I checked all the fuses, and the level switches seem fine. My battery compartment is not wet, so I don't think it's the control module.

Most posts I have read indicate low or leaky air shocks, my case seem that the ride stays high all the time.

I hear the pump start up, so I know thats working.

Can anyone tell me what part of the system is not working? The level sensors, or the control unit, is there a way to test these parts?

Thanks