BMW E70 Rear axle Air suspension

Alan Gunn · Post by **Alan Gunn** » Wed Oct 07, 2026 6:04 am

Some years ago now when i changed one on my 2002 x5 i didn't know any better and got a low cost one from ebay or Amazon and it is still working now.
It was 8 or 9 years ago.

Greydog · Post by **Greydog** » Thu Oct 08, 2026 8:26 am

Well after using just about every source for information I can find or think of I am wondering why something so simple have to become so damn complicated ?? Through an ex- neighbour who works for BMW I have a 200+ page document on Advanced Diagnostics using ISTA and ICOM, today I should recieve my new EHC. So the plan is fit and calibrate the the New EHC (a simple process using ISTA) if that doesn't do it from what I have read there could be an issue with the Bus system between the EHC the FRM and JBE. This could be a resistance issue caused by a failing termination resistor or as daft as a poor earth point or corrosion in one of the Bus splices.
Then there is always Springs I am beginning to understand why so many X5's and RR end up on springs instead of air

Leslie · Post by **Leslie** » Thu Oct 08, 2026 3:56 pm

Don't give up bud you have got this

stick it on see what the reading is , if its still -127 it ain't that and no calibrating will sort it .

Greydog · Post by **Greydog** » Thu Oct 08, 2026 5:53 pm

Thanks for the support Leslie
Well it wasn't that EHC made no difference !!!!! So back to reading and learning about BMW Bus Systems and it is an eye opener for me to say the least. So how many Bus systems are operating in an E70 ? Ten, D-can, K-can, PT-can, F-can, Flexray and Most then in the back ground Lin-Bus K-Bus BSD and Lo-can
The MOST system I can ignore at the moment as that deals with Information systems Communication and Entertainment So I need to concentrate on the Flexray, (Star System) F-can and K-can (are Linear 2 wire systems) Flexray links the suspension EHC and sensors to the Vertical Dynamics Management Flexray is linked to the rest of the car by K-can and F-can once I get my head around the architecture and how to measure each systems noise levels I may be able to separate them and isolate the culprit. Thought I had given this up when I retired

Leslie · Post by **Leslie** » Thu Oct 08, 2026 6:56 pm

what does the right rear read when you unplug it ?
Are you sure the lines to the compressor are refitted correctly incase its pumping the wrong side ?

Greydog · Post by **Greydog** » Fri Oct 09, 2026 8:39 am

Morning Leslie
Unplug the sensor and get Suspension Inactive on the screen and dash plus fault code 059F if I recall correctly
As I read/learn more about the way BMW configure the Bus architecture I am leaning towards a fault/failure some where in either the K-bus or F-bus. It is possible that a Termination resistor has started to fail I hope that isn't the case as apparently they are located on the PCB inside end of line Control units. As I am not seeing other faults and from what I am reading the K-bus will still communicate on one line just at reduced capacity and speed either side of the damaged area. So todays fun task is to try and locate all K-bus splices close to the Flexray connections. Then go digging in the loom to find them.

Leslie · Post by **Leslie** » Fri Oct 09, 2026 12:03 pm

Are there any earths at the bottom of the rear fusebox or in the bootfloor ? , I still think/hope it will turn out to be something simple

Greydog · Post by **Greydog** » Sat Oct 10, 2026 8:30 am

Morning Leslie
Yes 3 multiple Earth points in the boot that I am aware of so today I will remove them clean the area apply a little electrical contact paste and remake the connections if it works I will kick myself

While I am in there I will check the K-bus Node points in the boot loom, I did repair one of the larger points soon after buying the car. From the schematics I have obtained I have some clues to where they are it is just finding them as they are wrapped in the main loom. The next Node point apparently is near the B pillar so some trim to remove then dig under the carpet for the loom. BMW favour a compressed crimped join that works until it gets damp then they seem to corrode quickly, resistance goes up disrupting signals. On the plus side I now have documents on the Bus systems and their achitecture plus advanced diagnostics so if anyone here fancy's a headache I am happy to share

To run full diagnostics on the bus systems the oscilloscope in ISTA isn't capable so I will need to borrow one from an engineer who used to work for me if that is needed.

Leslie · Post by **Leslie** » Sat Oct 10, 2026 5:13 pm

Wow this sounds more like rocket science every day, I feel like I need to go back to school for a refresher

have you had any water leaks in the past as that's where corrosion is most likely to start ? I guess checking the last known faulty point and indeed areas near it is the first port of call , lightening can sometimes strike twice

I think we are entering the Master tech zone

X5Sport · Post by **X5Sport** » Sat Oct 10, 2026 6:45 pm

When you need a degree in Computer Science, advanced networking and automotive engineering, it’s time for another beer….

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