Rear ride height malfunction

[lchurch]

Walked out this morning and found the back end of my 99 540iT jacked up to the maximum height on the suspension. So some thing(s) have failed in the auto air shock system. I think I have identified four possible culprits:
1. The ride height sensors. Makes sense except that both sides are up, which implies both sensors are to blame. Not likely.
2. The electrical relay controlling the pump has latched "ON", meaning the pump is merrily pumping air into the system no mater what.
3. The two electrical solenoid air control valves, one for each rear wheel, are jammed.
4. The control module has gone over the edge.

The system is pretty straightforward, not necessarily typical of BMW. What nothing in the write-ups I could find was "how and where is excess air bled from the shocks?" If I load the back with 400 LBS of beef then it's easy to understand that the ride height sensors would issue a call for more air. But when I remove that extra 400 lbs. I would assume the air bags would shoot the rear end up, at which point something (I would assume the control module) would reduce air pressure until the ride height sensors read normal. But what mechanical part actually valves that air out of the system? The solenoid air control valves?

I'm headed to my local independent shop late next week after a quick trip out of town. He will slip the BMW diagnostic computer on the system and see what it can tell us. But I' like to have some more knowledge before I walk into his shop and perhaps a buzz saw.

TIA
Lee

[dannyzabolotny]

Yeah, sounds like the pump is just staying on too long because of some malfunction in the system. Hard to tell what the issue is until you plug into a diagnostic computer and talk to the SLS module. However, what you can do for now to get the rear back to a normal ride height and be able to drive the car without putting more stress on the compressor is to pull the SLS fuse in the trunk and manually bleed some air out of the system. You can do that by popping up the cargo floor panel and gently undoing the 10mm nuts on the air lines going to the air struts, that'll allow you to slowly release pressure and get your car back to a normal ride height until you can get it repaired properly.

[BimmerBreaker]

Relevant:

[StephenVA]

Air shocks !
People pay extra for that option.....

[dannyzabolotny]

Air shocks !
People pay extra for that option.....

It's an awesome system when it works, and it works like 99% of the time. It's awesome for hauling heavy cargo, which is kinda the point of having these wagons in the first place. An E39 touring without SLS is just like a heavier E39 sedan with a bigger trunk lol.