The rear driver's side of my X was sagging randomly, and I had the "self leveling suspension inactive" more than once over the last few weeks. But it would fix itself by turning it off, then restarting it. No error codes, and it most days the car remained level overnight. So I assumed the rubber of the original bags was just old. Bought new Arnott bags from Rock Auto for roughly $200. Took about 2 hours because I was doing it by myself. Not too hard of a fix. The hardest part was lining up the new bags to fit in the holes. A second set of hands would have saved me about 15 minutes of struggling. Put it all back together and everything worked perfectly! The pump fired right up, and the new bags are holding her level.

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2003 X5 4.4i, 6/03 build date