M001 is also the fusebox in the cab, by the driver's knee. In my LHD van it on the left side, I assume with the RHD it will be the driver's right knee. Check the owner's manual for localisation and access.
H115 is the air suspension control panel (a little higher than the fusebox cover).
Here's the diagram with the localisation of the air suspension elements:
And that's the link to the online eLearn, section about the air suspension on a x250 2.3 l diesel engine (which I took the diagram from):
