So now I have done several tests. First I disconnected the battery for 10 minutes. no changes. Then I arranged the relay and connect it again, no change. Then I connected the diagnostic device. The controller detects any height sensors.

The computer measures a change in nominal ride height under load only the front left(when I step on the footboard ).

Front right, rear right, rear left are always 0mm difference to the nominal height.

Ok, now I think of course the height sensors are faulty. But why do they still change their voltage?