The brief
Peter's 730i was sitting slanted, leaning down on one rear corner, especially after it had sat overnight. He brought it in. On a 7 Series that's the air suspension telling you one of the air springs has a leak. These cars ride on air springs instead of conventional steel springs, fed by an onboard compressor, with a control system that keeps the car level. The air springs are a rubber bladder, and over the years the rubber perishes and cracks, so it leaks air, and the compressor can't keep up, so that corner sinks and the car sits slanted. A leaking air spring doesn't reseal, and the compressor working overtime to fight a leak wears out too, so the failed spring needs replacing and the system recalibrated.
The diagnosis
A check confirmed it, the air spring on the low rear corner was perished and leaking, holding air for a while then sinking, which is exactly the slant after it sits. The compressor and the rest of the air suspension were checked and were sound at this point, so it was that one air spring. That's an air spring replacement on the affected corner, you don't patch a perished bladder, so the call was a new genuine BMW-spec air spring, fitted and the ride height recalibrated.
The work
The old leaking air spring was removed and a new genuine BMW-spec air spring fitted, the air line connected up cleanly, every fastener torqued to spec. The air suspension system was then run up, the ride height recalibrated through the proper procedure so the car sits level, and the stored faults cleared. A road test confirmed the car sat level, held its height overnight, and rode as it should.
The outcome
The car sitting level on all four corners, holding its ride height, riding the way it should, and the air suspension faults cleared. The 730i went home with the air suspension sorted. A leaking air spring only sinks worse and wears the compressor out chasing the leak, so changing the spring and recalibrating the system put it right before it became a bigger job.
