Self-leveling rear suspension concerns

Multibeemer · #1 05-29-2012, 08:10 PM

The dreaded "Self-leveling Susp. inactive" warning light came on our 03 4.4i (102,000 miles) several days ago, and hasn't gone out. It typically comes on after about five minutes of driving, and then stays on.

But of greater concern is that my daughter heard a pronounced hissing sound coming from the right rear of the vehicle this morning, after having sat all night. She said it sounded like air leaking from a tire. This makes me think the warning light is not a false alarm.

The car's ride height visually looks OK, so I measured from the ground to the bottom of the fender, and here's what I found:

Right rear = 31-7/8"
Left rear = 32-1/2"
Right front = 31-1/2"
Left front = 31-5/8"

So it is sitting a tad low at the right rear, but these measurements were taken on a sloping driveway, so they may not be perfectly accurate. I took it for a drive tonight, including going over several speed bumps at the nearby middle school, and the vehicle drives fine, as far as I can tell. Any thoughts on what I should look for by way of troubleshooting? What could have caused the hissing? Is it safe to drive? Thanks.

FITZUNI · #2 05-29-2012, 08:55 PM

BMW Air Suspension Parts & Kits - Arnott Industries

FITZUNI · #3 05-29-2012, 08:56 PM

$200 rear air springs....

Multibeemer · #4 05-29-2012, 09:21 PM

Thanks; that's a very reasonable price for the air springs, and they come with a lifetime warrantee. But do you think this is likely my problem? If my air springs are worn, would they likely hiss? The car has air springs only on the back, so doesn't the fact that the ride height is virtually identical front to back suggest that the air springs themselves are actually OK?

And what typically triggers the "Self-leveling Susp. inactive" warning? The spring itself, or something else? Thanks.

mike_dmt · #5 05-29-2012, 09:42 PM

5/8" is more than a little IMO, so, a little investigation will go a long way. I believe some of the system is in the spare tire well. But if your daughter heard it outside of the vehicle, and on a specific corner, that's where I would look.

Did she hear it first thing initially after start up after sitting for a while? After running and driving for a while, and continually trying to level itself? Both might indicate a leak somewhere in the system, but if the air spring itself had a puncture or something seriously wrong with it, the compressor would run fairly often, if not non-stop.

The next thing to look at might be the air lines and connections themselves. Some soapy water applied to the connections might point out a leak...

Get a little dirty, and save a lot of $$$

rogerkiu · #6 05-29-2012, 10:30 PM

I believe that what your daughter hear is the pump was working to pump up the rear air bag, not hiss. To corrrectly measure the ride height, first you need to measure the ride height immediately after you park your car after driving, and then measure again before you unlock your car after sitting overnight. According to BMW's info, for 20" rims, the ride height for sports setup is 708mm (+/-10mm max.), for non sports setup is 731mm (+/-10mm max). You need to measure from the lower edge of your rear rim to the edge of wheel arch trim. If you are using 19" rims, the ride height is 720mm, 18" rim - 709mm and 17" rim - 698mm.

mike_dmt · #7 05-29-2012, 10:41 PM

I agree with rogerkiu, to measure the ride height before and after driving. But my compressor never "hisses". It just sounds like a compressor..

What if she was hearing the fuel pump?.. I haven't had to get that deep into my X yet, but the one in my E36 almost sounded like it was hissing..

Still doesn't explain the 5/8" difference though.

Multibeemer · #8 05-30-2012, 12:00 AM

Thanks for all the tips - good stuff. To answer the questions, she heard the sound first thing in the morning, after the car was sitting overnight. It hadn't been driven in about 30 hours. She described the sound as like air being let out of a tire, which I would interpret as a hiss; I wouldn't think a compressor would sound like that, but this can be pretty subjective stuff. And it can't be the fuel pump, because the key wasn't in the ignition - the car was locked.

I'll measure the ride height as rogerkiu describes, and I'll do it on a level surface this time. Checking the air lines and connections is a very good idea, too - sure would be nice if the whole problem is caused by a loose fitting.

civdiv99 · #9 05-31-2012, 01:55 AM

Check the little black air lines at connection points in trunk well. Wiggle (gently) and listen.

Cole · #10 05-31-2012, 07:35 AM

If you have a small leak in the air spring the pump will have to work extra to maintain the ride height and this could trigger the warning message. If the leak is such that the air only escapes when extra pressure is exerted, then the X could still maintain level when parked, but perhaps the air only starts escaping when you load the air spring a little and it flexes. That could explain why your daughter heard it hissing when you started moving...