I've been having a bit of bother with the air suspension on my F11. It's complicated so be warned this could be a lengthly post.
I think it started maybe a month ago. Soon after setting off from home I noticed a different feeling at the back of the car. There's an uneven piece of road I drive over 1/2 a mile from home anything over 30MPH loads up the suspension quite effectively and when passing over this it felt as though the suspension was compressing more than usual, possibly even touching the bump stops. By the time I'd got to the T-junction another 1/2 a mile along the road it had sorted itself out, feeling as normal and no visual sign of dropping. I made a mental note to keep an eye on things and see what developed. I had a similar feeling a few days later but again it didn't last long.
Then as luck would have it I found I had a broken front spring so ordered a pair of Eibachs and carried on using the car gently to get to work and back. Once the springs arrived upon leaving the house on the way to leave the car at the garage to have them fitted I felt the same feeling over the uneven section of road but this time it didn't sort itself, getting steadily worse until the idrive lit up with the Chassis warning - Drive moderately etc.
I was able to pull in to a lay-by not far down the road, switched off the engine and jumped out to have a look. The was sitting low down on the right rear corner, more so than the left but that might've been as much to do with the ground where I'd parked. I decided to restart he engine and continue driving moderately to the garage. Upon restarting the car lifted immediately and drove to the garage without further issue. I told the garage what had happened and asked them to have a look at the rear suspension while the car was with them.
When I returned to collect the car it looked to be sitting lower at the back than usual. The garage agreed and said they'd found a bent height sensor bracket on the right rear corner and a fault code indicating the compressor had timed out after having to pump for too long trying to level the car. They suggested fitting a new bracket before going any further. It was only a fiver so I agreed. They had to order it from Germany so it took a week or so to arrive. They tried bending the old bracket back to roughly where it should have been before I left. The car responded by lifting slightly but was still a bit lower than usual and after leaving garage it sank lower. I continued to use the car carefully while waiting for the new bracket. The ride at the back felt different, not as firm, as though the rear suspension was not supporting the car quite as solidly as before and felt as though it had a greater tendency to squat down closer to the bump stops when going through certain dips in the road. Otherwise it wasn't too bad for a day or two but following a longish trip across country to collect a car for our daughter the ride was deteriorating quite badly. I'd been looking forward to the drive but in the end it was no fun at all. We got back too late in the day to investigate but the next morning I jacked up the back of the car at both sides in turn, removed the wheels and had a good look round for any signs of something amis. The ride had been so bad I was sure I had burst a shock absorber or something equally as drastic. I didn't find anything so just had to put the wheels back and head out to work. The car drove perfectly 45 miles each way, as though the lifting of each rear corner from the ground had reset something. I was looking forward to driving back to work the next day but 1/2 a mile from home the dropping and chassis warning were back. I'd already done a bit of searching online for clues to what might happening. I stopped and it was clear both sides had dropped. There's a lot of posts on our great forum here regarding rear suspension woes but I couldn't find anything which seemed to describe the symptoms I was getting. Widening my search I found an interesting thread here... https://www.bmwland.org.uk/index.php?threads/f11-air-suspension-sticky-thread.1477/
which seemed to describe a very similar problem to mine, as far as the dropping was concerned anyway. On the basis of this I decided to get the car to lift up then remove fuse 152 in the hope it would disable the Electronic Height Control, prevent the dropping and keep the car drivable until the cause could be narrowed down. I restarted the engine, listening under the back of the car I could hear the compressor running as the car lifted, and then a slight psshh as it cut off. I pulled the fuse straight out and I carried on driving.
With the fuse out there was no dropping at all either when driving or parked up. I took height measurements at various times which varied slightly depending on where the car was parked but averaged out at roughly 590mm. That's about 30mm lower than it should be. It was fine for several days as long as I was careful to avoid loading the suspension too much, no dropping when driving or parked so I was reasonably satisfied there were no leaks from the air springs or lines.
I ran the car like this for a few more days until the new height sensor bracket arrived. On the way to have it fitted I stopped and refitted fuse 152. The car immediately dropped again, this time right down to the stops. I had to mess about for 15 mins, switching off and back on again, opening and closing doors and checking fuses before the car lifted again and I could get to the garage. On removing the old bent bracket they found the joint between the end of the sensor and the bracket had seized and suggested that might be what had bent the flimsy Aluminium bracket. They fitted the new bracket, reconnected the sensor and checked for any fault codes. All good but the car would still not lift up to it's proper height. The garage thought the compressor might be failing internally and so not able to fill the air springs sufficiently to lift the car to its set height which might explain the compressor time-out fault code. They wanted to wait for an email with some details on what sort of pressure values the compressor should be achieving before they could investigate any further and I needed to get to work so I took the car, leaving fuse 152 in place to see if the new bracket would make any difference. It was still low but wasn't riding on the bump stops, there was still room for the suspension to move with the road surface and as long as I drove moderately it was ok. I made it to work and back and felt ok about doing the same the next day but during the course of my journeys the ride got progressively worse and driving back towards home it felt like the car was more or less on it's bump stops most of the way. This was late on Saturday afternoon. I called at the garage which is on my way home and caught them leaving for the day. Nothing they could do then so I just limped slowly home planning what to do about getting to work the next day.
A plan formed. When I got home I jacked up the back of the car and pressed on the bellows on the air springs. They were soft, right side slightly softer than the left not totally empty but nowhere near as firm as they're supposed to be. I decided I'd try using ISTA to tell the compressor to run and see it I could get some air into the bags. That worked, after a fashion. The ' Inflate Air Bellows' command in ISTA runs the compressor for 40 seconds. The compressor started and ran as expected and both air springs were nice and firm so I let the car down off the jack expecting it to find the correct height, or at least attempt to find a height it thought was correct. It didn't, with the weight of the car back down fully on the wheels and engine running the back of the car was sitting up high looking like it'd been customised for off roading and making no attempt to adjust itself. Not ideal but at least I knew the compressor was making enough pressure to fill the air springs. I got the car back on the jack again and started ISTAs 'Bleed Air Bellows' procedure which worked as expected and both springs were completely empty. I started the Inflate procedure again but this time counted for 20 seconds then switched off the ignition. The compressor cut off. I pulled out fuse 152, lowered the car and was glad to see the car sitting at a more suitable height for driving, still a bit lower than it should be but a vast improvement.
The car stayed up all night and I've driven to work and back today without further issue.
For the time being I'm going to run the car with fuse 152 out and try to get round to some further diagnosis.
So now I'm wondering where to go from here.
It seems there are no leaks. The car only drops when fuse 152 is in place which suggests to me a problem with the EHC module or the discharge solenoid valve.
If there are no fault codes associated with the EHC module the does that mean the problem must be with the discharge solenoid?
But then why did the car not try to lower itself to the correct height after I inflated the bellows the first time? There might've been a fault code left from running with with the EHC fuse out. Would that be enough to prevent the system trying to level the car? Do I need to make sure all the codes are cleared before expecting the EHC to work properly?
Have I actually got two simultaneous problems, the dropping and the low ride height with two different causes? Too much of a coincidence?
The Eibachs fitted to the front are lower than the standard so would that have any effect on the rear? One question which crossed my mind was would the car automatically try to compensate at the back for the lower ride at the front? No, I don't think it works like that. My understanding is the rear ride height is programmed into the system and that should be what the car aims for independent of any changes the front.
Well, apologies for such a long and rambling post. As you can see there's been quite a lot going on. If anyone's still reading after all that any thoughts would be welcome. Any pointers on where to look for further diagnosis before I just let the garage deal with it?
Just to add the car is a 2014 LCI F11 with 111000 miles. Air springs are roughly 2 years old with 40000 miles on them. Any advice appreciated.