different air suspension pain 4.8is

[TwinsPoppa]

Control Modes (See attached for flow chart)

Sleep mode
If the vehicle is parked, it enters Sleep mode after 16 minutes. No further control operations are executed. A "watch dog" wakes up the control unit for a few minutes every 6 hours (wakeup mode) in order to compensate for possible inclination of the vehicle. (Vehicle height may only be corrected once as air supply unit only operates with engine running.)

Wake-up
In wake-up mode, the control unit is woken up for a set period of time in order to compensate for possible inclination of the vehicle. Inclination of the vehicle can be caused by large temperature differences or by minor leaks. Adjustments to the front and rear axles ensure that the vehicle is visually level. To minimize power consumption, the vehicle is lowered
only. The nominal level of the lowest wheel serves as the nominal level for all other wheels. The lowest nominal level to which the vehicle is lowered is the Access level (-35 mm).

Exception:

if the vehicle is parked at Access level, the vehicle is lowered to max. -50 mm in wake-up mode. If the vehicle is parked for a prolonged period of time and there is a leak in the system, further loss of pressure does not produce a change of ride level since the weight of the body is born by the auxiliary suspension and the residual tire pressure.

Advance /Overrun

When the vehicle is woken out of sleep mode by the load-cutout signal (VA), it normally enters advance / overrun mode. Since the engine is not (no longer) running in this mode, however, there are restrictions on the control operations that can be performed in order to conserve the battery. Ride level compensation is restricted to tolerance ranges of 20 mm and 25 mm in the up and down directions respectively. This serves to reduce the frequency of control operations. All control operations in advance / overrun mode are executed as long as pressure is available in the accumulator. When the accumulator is empty and the engine is turned off, control operations are directly driven by the compressor. User-activated changes of ride level and filling of the accumulator are not possible.

So, after 15 mins, X goes into Sleep mode. After 6 hours its supposed to go into Wakeup mode and compensate as long as there's enough pressure in the Pressure Accumulator. Have you observed what it looks like overnight (after 6 hours)?

If your X tries to correct the ride height after 6 hours, but does NOT, then maybe there's not enough pressure in the Accumulator because either its faulty or the compressor in the Air Supply unit is bad (could not pump enough pressure into the accumulator before going into Sleep mode). I assume that the EHC2 module (Control Unit) is working properly as this is what gives the commands and the rest of the system executes them.

This still does not point to where the problem is exactly. This is also assuming there's absolutley no leak (which is still my best guess). I know, lots of assumptions.

Okay, so someone correct my thinking or feel free to comment.

[civdiv99]

Rear bags are independent but fronts do have lines in common. Start checkin' connections from the accumulator (ok, it's an air tank) under the car on fwd.

Originally Posted by pieter4458

I recon that if both air bags goes down simultaneously it can not be them and suspect the lines. But it can happen that they are both bad and will test with soapy water.

[pieter4458]

I checked the two front lines at the control valve, next to the accumulator and could not find any leaks. The next step is to check the line connection on the top of the airbags for airleaks. If there is nothing, then the only culprit can be the airbag itself that is leacking (slow puncture).

I am afraid to use the car at this moment as the movement on the airbag can sqeeze air through the small punture and the pump keeps on working to compensate - it may burn out.

What puzzles me is why is the car dropping in front to a certain level and then it settles. Can it be that the small hole in the bag folds to a point where it seals and why both sides?

[TwinTurboGTR]

Bingo. I am sure if you left the car sit for 48 to 36 hours, the system would be completely slammed.

[pieter4458]

Originally Posted by TwinTurboGTR

Bingo. I am sure if you left the car sit for 48 to 36 hours, the system would be completely slammed.

This is the funny point, it does not go lower than a certain height, even if it is parked for 2 weeks. I did this last month and then after 2 weeks the famous "air suspension inactive" message came up. Then I had to reset it again!.

If I leave it again I suspect this message will come back again.

[civdiv99]

Well, this is what I would do:

Remove your rear load floor components so that lower area is open to the cabin. Fold your back seats down. Now go about your regular business, but with your radio and fan, etc. off. If the compressor is always kicking in while driving down the road, then you have an issue which may or may not be urgent depending on the frequency (it's a relative thing I suppose). If it kicks on rarely or not at all, and therefore it's just compensating each morning or whatever, your urgency level just dropped quite a bit.

Originally Posted by pieter4458

This is the funny point, it does not go lower than a certain height, even if it is parked for 2 weeks. I did this last month and then after 2 weeks the famous "air suspension inactive" message came up. Then I had to reset it again!.

If I leave it again I suspect this message will come back again.

[TwinsPoppa]

Originally Posted by pieter4458

I checked the two front lines at the control valve, next to the accumulator and could not find any leaks. The next step is to check the line connection on the top of the airbags for airleaks. If there is nothing, then the only culprit can be the airbag itself that is leacking (slow puncture).

I am afraid to use the car at this moment as the movement on the airbag can sqeeze air through the small punture and the pump keeps on working to compensate - it may burn out.

What puzzles me is why is the car dropping in front to a certain level and then it settles. Can it be that the small hole in the bag folds to a point where it seals and why both sides?

The leak may be so miniscule, for now, that your last point is what's happening.

As for why its leveling on both sides, it just may SEEM to be both but can be only ONE having the leak.

Here's why, after 6 hrs:

Wake-up
In wake-up mode, the control unit is woken up for a set period of time in order to compensate for possible inclination of the vehicle. Inclination of the vehicle can be caused by large temperature differences or by minor leaks. Adjustments to the front and rear axles ensure that the vehicle is visually level. To minimize power consumption, the vehicle is lowered only. The nominal level of the lowest wheel serves as the nominal level for all other wheels. The lowest nominal level to which the vehicle is lowered is the Access level (-35 mm).

IMO, I think there's nothing else going on here but a leak in one of your air struts.

[mikeinmn]

Thanks for the attachment TwinsPoppa! Good data. Knock on wood, mine works perfectly... other than it sometimes raises itself as if I had hit the up button but didnt. Once when towing my boat, pulled into the driveway and she was up all the way! As I looked at it wondering WTF, it dropped itself back down. Other times the front only will raise as it sits for a while. I'll pay more attention to the length of time as that seems to matter according to the data you posted. Thanks!

[Christiano]

Man, you have a bag leak, IMO. Mine does exactly the same thing...

[sockethead]

I found that when the air bags wear out, it's not really a hole per se, the bag it literally worn out and a whole area will become porous. When you spray the bag with soapy water, it may not just bubble up in one spot like it would with an obvious hole, it will kinda foam up in the area that has become porous.

How are you resetting the inactive warning? do you have DIS? If so, that will tell you why the message came on in the first place. Then you need to run through the test plans. It should have a test plan already loaded from the error. It tests compressor, Accumulator fill and vent and a few others if I remember correctly.
You can also test individual components.

Intermittent issues like you are having can be very frustrating. Our 4.8 has had the inactive warning for about 6 months. DIS reports that the error is an accumulator fill error. After extensive testing by me and BMW, we all *think* that the compressor may be weak but we're not willing to spend $500 to find out so I live with the error on the dash. All of the air bags have been replaced as they failed one right after the other.