G31 rear suspension problem

Hi Folks - new to this forum, greetings from the Isle of Lewis. My family car is a late 17 520d Touring SE (beside the R53 JCW and E36 M3) Brilliant car all round but since purchase (used) in Sept 2020 I’ve had a niggling doubt about ride height. At times low in comparison to tyres and other times “looked” higher than it should. After a return to dealer in May 2021 for another reason, I asked for suspension to be checked - “within parameters and no fault”. Fast forward to recent weeks, ride height high with no‘self levelling’ or compressor noise. In last few days it has moved to a frankly scary height - there is about 10 inches from tyre to arch - and a chassis warning on idrive/dash. Any ideas?

 

I’d suggest you have a problem with the rear ride height sensor controller. There are two level sensors, 1 left & 1 right.
Both sensors connect to a system BMW term the Vertical Dynamic Platform, or VDP for short.

The VDP operates a block of air valves (amongst other things) that permit air to enter or be released from the bellows (air springs) supporting the car. Compressed air is produced by a little compressor unit and stored in an attached reservoir. The bits are located under the rear diffuser below and behind the bumper.

Information supplied by the level sensors (basically a pair of swivelling fingers) will tell the VDP where the car is sitting relative to its predetermined height.

If the whole back end has gone high in equal measure, that suggests the air valves have opened causing the compressor to run till it can pump no more.

The VDP module lives behind the wheel arch cover (LHS I think) in the boot. It’s a pig to get to!

There is nothing to adjust as it’s programmable. You need a workshop visit.

P.S My touring will sometimes lift her backend for no apparent reason when parked overnight. Unlocking the car seems enough for it to sort its self out and lower down a few seconds later, I'm talking 2" here and not a foot.

 

Hi John - thanks for taking the time to reply. Your information was really helpful and I took the car to my local independent bmw garage who connected up the gizmo needed - all sensors showed ok and clearing any faults (there was reference to an “if fitted (it isn’t) front sensor) made no difference. Culprit seems to be the compressor itself - the ride height was high (probably 5 inch) clearance on Friday but was double that on Monday- the air shocks are maxxed out. Car is undriveable, dangerous in fact. Strip out began today at garage but any hints and tips gratefully received. Incidentally, despite me raising this twice under warranty (and fobbed off) it is no surprise BMW won’t even discuss goodwill as used car warranty out in October.

 

Interesting. I had the reverse problem a couple of years ago with my G31 530d.

The back end went down over a week or so! The fault was traced to a chafed wire feeding the compressor which shorted out the feed resulting in it being shut down all together and a chassis warning on the iDrive.

Whilst researching the issue I came across a website called REALOEM which lists parts for BMWs. (See exploded diagram) A very useful resource.

The compressor is a self-contained unit and fairly ubiquitous across the model range. A new one from BMW will be pricey, a good second-hand one £250-£300, a Chinese one dubious quality.

I’ve attached some pics for you.

 

Hi again everyone…my G31 still in garage. Process of eliminating causes has failed to reveal problem. The control unit is dry, sensor checks show no faults, fuses and relays ok and compressor will kick in but not release! Compressor removal and inspection reveals its very wet inside everywhere - not great for 4.5 years and less than 50k miles. The solenoid is missing an o ring (found that was an issue for an x5) so drying out, new o ring and lots of crossed fingers tomorrow. Anyone else find that compressor keeps inflating without ability to release? Hoping to avoid new compressor, but Indy mechanic feels this most likely even tho it will pressure up. Thanks for the replies so far.
Iain

 

New sensors: no change. New compressor, seems to have fixed it. Much anger. Pleading letter to BMW in draft….2 grand and no faith in car now.☹️ 10th BMW but build quality not as it should be. Avant here I come…

 

Heads up for members - I have had an ongoing chassis warning light for about 6 months now. My car (2018 G31 520d) with 60000miles was recalled to the main dealer's in Poole for renewal of the EGR valve. when booking in at reception they noted the chassis fault in the log but after inspection they found no issues and advised that they had wiped the log. Driving home from there the warning light came on again although there was no misbehaviour of the suspension. Long story short - I took the car to "Burch Motor works" a BMW specialist in Christchurch to investigate. they took the time to look at it properly and discovered that that one of the relays was showing a lot of arching damage and consequentially the compressor was getting intermittent feed. The diligent people At Burch replaced the relay and all is now good. great result for less that £120. So if you live anywhere near Christchurch on the south coast Burch are the people to see. PS. I have no connection to this Garage I am just very please at the great service.