air suspension pump problems 4.8is

[pieter4458]

I sit with a problem that is not the normal air strut leaking or car lowering problem, but the following:

1. The suspension height level stays constant at 715mm over a period of 2 months. The only change I can see after a drive is +-5mm on any side.
2. The air suspension inactive warning is on and the height control switch is inactive.
3. when getting into the car or switching ignition on, the pump can be heard for a few seconds and then stops.
4. The height back or front stays the same, regardless if the pump works or not.
5. Removing and replacing the 30A and 7.5A fuses have no effect at all
6. When doing a air suspension "reset" with the normal dealer software (GT1) reveals a error with the filling of the compressor and inactive pump.
7. The reset only last a day and then the inactive air suspension message comes back and an inactive control height switch.

My problem is that i do not want to buy a new pump if it is the air suspension control unit and vice verse. It can also be the pressure switch?

My car is the 4 corner, dual axle type.

WHERE SHOULD I START LOOKING FOR SOLVING THIS PROBLEM?