BMW E39 air suspension: rear sinks overnight
E39 air suspension: why does the rear sink overnight?
Air is escaping from somewhere. Common leak points are a bellows with a hole at the fold, a leaking air tank, a leaking valve or a rusted pressure tank. If the system is in order, the rear must not sink after shutdown.
How do I find a leaking bellows or valve?
The bellows is removed and pulled out long, and the hole shows at the fold. The valve block cover can be opened: marks left by the needle in the counter-rubbers indicate a leak. A hiss from inside the wheel points to a leaking part.
The level control gives a warning right at startup - what do I do about the dryer?
The dryer beads can get damp, freeze and block the air flow. The beads are dried in an oven for about an hour and put back in the dryer. Cat litter is not suitable, because it turns to mush when damp. If the compressor works but the fault continues, check the height sensor and its wiring.
What is the E39 level control reference height?
The reference value is about 360 mm measured from the wheel centre to the wheel arch. The height setting is in the control unit's memory, so replacing the compressor does not change it. The level control does not affect the shock absorbers.