Swanny_UK

Hello - I've been looking through previous threads regarding the E61 rear air suspension, and they've been really helpful. I'd like to thank 02Dag for their really useful thread here, along with numerous other threads and users who've educated me to some of the other components and how they work.



A few months ago I got a slow drop of the back end, and after diagnostics using the manual activation in INPA, I found that the solenoid pack on the compressor had been sticking, so I swapped it over. All was fine until Sunday when the car started dropping, the compressor kicked in, and wouldn't turn off. I managed to coax the car home thankfully before it was on the floor. I had to pull the fuse (52) to stop the compressor, as it was getting really hot.

Having previously tested the components, I knew that the bags needed replacement, so I've replaced them with a pair of new ones. I reconnected the air lines etc, put the fuse back in, and the compressor started up straight away, but didnt start to inflate the air bags. With INPA attached, I manually raised the bags, you could hear the solenoids click, and the display showed them opening, and the bags inflated. I got them so they were both the same height, then raised and lowered the rear axle, each time the solenoids working as they should. However the compressor still runs constantly.

I thought that it might be the ride height control module at fault, but I can connect to it in INPA, and it controls the bags manually. I checked it wasn't in production mode, or garage mode etc, and it wasn't. With the compressor disconnected, the control module still controls the ride height correctly using the solenoids.

There were a couple of errors on the log (translated using google translate);

5F99 - Control Time Unilaterally Lift Rear Right
5F9A - Increase control time
5FB4 - Energy saving mode active

I thought it might be the green relay stuck on, but there's no continuity between pins 86 and 87 when its disconnected.

I'm a little baffled right now as to how to proceed further. Can anyone help?

Swanny_UK

I had left the relay unplugged overnight, not intentionally, an oversight on my part. A friend came round to help diagnose, with some tools from work, and the wiring was fine, he tested the relay, which was working fine, continuity when 12v applied etc. The battery was connected. Once we'd tested the wiring and the relay, I put the fuse back in, then the relay, and nothing.....

Which was exactly what I wanted, but no idea what the issue was. The car still goes up and down in INPA, the valves open and close, and when it needs the compressor it turns it on, its just not on all the time now.

So it seems to be resolved, but i've no idea how.

kd7iwp

Thanks for updating us. I wonder if somehow the relay got stuck in the closed position?

habbyguy

I think kd7iwp is correct. I couldn't find the schematic for the rear suspension circuit, so don't really know how it's controlled. But being a BMW, you can rest assured that it's much, much more complicated than it really needs to be. ;-)

At this point, I'd say the best approach is to pretend it never happened, but keep an ear open to catch a repeat. I suppose it's always possible that it might come on at some random time and run your battery down, but I'd guess it's only going to happen when you're actually using the car.

wkloppen

The level control module is in the trunk as well as the relay. Remove the connector and check the pins for corrosion. Might be nothing but the mere unplugging and pluggin it in again might just help a bit preventing another going astray behaviour

reg

w.

habbyguy

Relays - particularly those supplying power to inductive loads like motors - are prone to "contact welding", where the current passing through the not perfectly closed contacts produces enough heat to weld them together, tightly enough to overcome the weak spring action that is designed to separate them when the relay is turned off. Sometimes this will happen once, but it tends to be a more common thing after it does happen once, as it means that the (usually) gold plating has been compromised, allowing a poorer, higher-resistance connection to occur (which increases the potential for contact welding). A new relay fixes this, of course.

wkloppen

well said. Can't be explained much better then this....

actually I'm due for either a new compressor or valve unit or both. The airbags are new but once in a while it takes too much time to get the rear on level so either a worn out pump or a valve unit.