Xoutpost.com - self level susp inact message display

Copy the following posts out by pasting to word and take it in to your dealer. In fairness to them, when I went in they had no problem replacing the parts but weren't aware of the details as BMW will not post out a service bulletin that I know of. I have not had any problems in some months and my car handles a lot better.

Cheers

Some of you may remember my earlier postings about the DME problem I had with my car and one of the symptoms being a change in behaviour of my suspension.

Well it seems I still have a problem of sorts although not catastrophic it is nevertheless irritating.

Normally with a 4.8is when you steer into a corner the car tracks very precisely with almost no body roll. You can tell this because it feels astounding particularly if you're used to how X5s usually drive.

The symtoms of my problem are evident (to me) that when I turn into a corner, the first 15 degrees of steering input causes little change of line but my car leans over a bit and then when it enters the curve I can feel the nearside front wheel loading up and losing the cornering line. Often I need to lift off and bring the car back on line to complete the corner. I also notice an unsettled feel when driving in a straight line whereby I am making constant little corrections. By comparison when it's working normally, the car just feels planted and tracks straight with very little input from the steering.

I've taken the car in twice in the past few days and had a DME log dump to spot any error messages. There is a fault code concerning the "exhaust flap", which on the face of it would seem unrelated but whenever I leave the workshops after they have reset my DME my car handles as it should with the suspension feeling perfect. This lasts for about 48hours until something happens and it reverts back to problem mode, with this "exhaust flap" fault code appearing yet again on the log.

Has anyone else noticed this kind of problem? It's perhaps not the kind of obvious fault that everyone would notice. Being a race driver and hyper sensitive to steering/handling balance I'm a bit obsessive about these things, but it's definitely happening to my car. Perhaps if you're noticing that your 4.8is feels a bit less agile or shows more body roll than normal it might be worth just checking your car out too.

My dealer and I are trying to find out what kind of sensors are used in the 4.8is and therefore how would the DME know if there was a minor fault. Perhaps something in the 'automatic self-levelling' system is faulty. It seems to be electronic since it's always cured by a reset of the DME but it's as usual very hard to get the information out of BMW in Munich to help diagnose the problem.

It's the kind of problem that most drivers probably wouldn't realise they had, and just like my 128mph speed limiter problem I find myself exploring new ground, initially receiving denials from BMW that anything could be wrong before finally being treated seriously. Wish me luck..

Zeke, there shouldn't be any body roll in the 4.8is. Mine doesn't this morning (I've just had it reset for the 3rd time this week) but I know that it will start playing up again by tomorrow. The 4.8is should feel fantastically nimble compared to any other X5.

The frustration I have is that it seems none of the faults with my air suspension or DME have ever showed up as fault codes on my error log. It seems to me that the control systems use slightly different protocols to communicate with the DME and some information gets lost. I'm trying to get this resolved with BMW GB and if possible initiate a fix for all cars that have been supplied to customers (whether or not they have had a problem or not).

I haven't had a proper de-brief yet but the suspension issues seem to stem from a problem at the factory, when the cars come off the production line they are set-up by technicians with all the base parameters. It seems that my car wasn't properly set-up and therefore the DME and all other control systems have been working off a corrupt baseline. Not sure exactly how it works but it seems to be something along these lines. I'm still pushing for an explanation as to why such errors were not logged in the DME and how we will ever know if it's properly sorted (without a weekly trip to BMW GB for a checkup). Also it seems that whilst the 4.8is is supposed to have a dynamic ride height capability, my car hasn't been functioning properly. So the rear ride height would be adjusting for load and roll whilst my front wouldn't, hence creating the inbalance and unusual pitching as I turned into corners. Again, I would like a proper technical explanation to assure me that it can never happen again, so I will reserve judgement until I receive this. The BMW technician has now changed tact from the diagnosis earlier last week and decided that the control-units and actual physical suspension components are fine, so the problem is purely 'software' related.

UPDATE: After 2 days in the workshop my car has returned. I'm hoping this is now 'near' to a final diagnosis of what went wrong with my car and therefore those of you that have contacted me can use my case as a baseline for any issues you may have.

The air suspension faults were a little more complicated. After working through several test schedules which incorporated various setup routines which monitor reaction time of suspension, geometry, adjustability and performance as a precaution the suspension control unit (this is were the faults are stored if any) was replaced. The car was set up again and responded accordingly.

Later on the BMW techie discovered from his notes that there may have been an intermittent fault with the original (main) control unit. He refitted the old unit and proceeded with some functional tests until he could reproduce any anomalies, this showed that the front suspension was malfunctioning. From his notes he was able to determine that the original control unit was interpreting information from the various suspension sensors incorrectly and sending out incorrect instructions. As far as the control unit was concerned there were no faults as it assumed all was normal. The new control unit was fitted and the suspension setup was performed again (this was at 7.30 last night!).

It was all powered down last night and this morning was checked to ensure it had remembered all the parameters, which it had.

Originally it was thought that the front ride height control (EHC) unit needed replacing, but this was a red herring, the actual problem seems to have resided with the main control unit which coordinates the actions of the ride height control units on each axle together with the actuators for each individual air spring.

I learnt some interesting things; apparently this main suspension control unit wakes up every 6 hours to check the suspension parameters and makes any necessary adjustments whether the ignition is switched on or not. So for example if you left your car parked on a kerb it would wake up and eventually adjust the suspension to level out the ride height.

The suspension control unit works constantly to equalise the ride height but also to stabilise the suspension should one strut pitch more suddenly than another. So for example, attacking a corner it will minimise dive and maintain the height of the nearside wheel whilst avoiding lift (and hence yaw movement) on the outside wheel. Hence the car feels like there is virtually no body roll.

Air Suspension

From what I can understand the faults in my air suspension system arose due to a faulty central suspension control unit. There are three control modules in the suspension system, one on each axle controlling ride height and yaw between each pair of wheels and one central control module that controls the balance of these settings between each axle and the overall stability of the chassis. This central suspension control unit also directly interfaces with the DSC control unit, which in turn interfaces with the engine DME and can cause the ignition timing to be retarded if necessary to improve stability.

My central control unit was replaced back in December 2004 which improved stability but still left a large amount of yaw when cornering. It is suspected that because the faulty control unit allowed too much yaw, this in turn damaged the front air springs. The complete front struts including air springs and dampers have now been replaced on my car and once these have bedded in and the central control unit has established a new threshold map, the air suspension is now controlling the chassis as good as any 4.8is that I've driven.

Either there is no fault code designed for a faulty suspension control unit, or the control unit only fell outside acceptable parameters on an intermittent basis and therefore didn't stay within this faulty zone long enough for the code to be logged.

The suspension performance is now vastly different to how it has been these past 6 months, it feels like the centre of gravity of the car has been moved 12 inches lower and there's no very little yaw and pitch when cornering and it truly defies the mass and size of the car. Now my car corners every bit as roll free as a Cayenne TT, but with much better feel and balance.