SLS / EHC I System Overview and Typical Failure Modes

[geargrinder]

Overview:

The SLS, or more technically properly "EHC I", system found in all USA 540 Tourings and some I6 Tourings - despite being highly maligned by the ignorant - is actually not a hugely complicated system, is not unreliable at all, and those things that do most commonly go wrong tend to be easy to fix.

Unfortunately crapbag mechanics with general hatred towards self-leveling systems, and general internet mis-information and conflation with other OEM's systems (ex:Audi & MB systems which ARE expensive and more complicated / involved to fix…) have screwed more than a few owners over. It is not uncommon for mechanics - even "BMW Indys" - mis-diagnose these systems, and cost owners giant piles of dough while failing to fix them. Cars continue turn up on the used market with their systems stupidly mangled or with an expensive brand-new pump assembly, yet still not working, because a mech or owner couldn't be bothered to learn about how the system worked and properly diagnose and fix it.

Some owners as well have a deeply-ingrained illogical and fact-free hatred for self-leveling systems and therefore go storming straight into spring conversions based on faulty beliefs about cost, reliability, and performance… Spring conversion is perfectly fine and for ultra-performance builds might indeed be the way to go, but there are few situations where cost and 'sensible maintenance logic' truly justifies not fixing the SLS - say unless perhaps the entire spare tire wheel has been flooded ruining the pump assembly and module,or some previous owner has chopped out all the wires and hoses and components and ruined the car already…

There's lots of good repair posts out there for specific bits, I won't try to make this an irritating linkfest but they are out there. Also won't get into how to lower the system for coilovers, suffice it to say there's 2-3 ways to do that between different link usage and using software to do it. Search around if you want that stuff.

At the bottom of this post are pictures of the overall system function. First a schematic showing the relatively straight forward nature of the components. Second, a drill down into the actual pump assembly and module connections. However in the 2nd case,those components very very seldom fail.

In the meantime,quick rundown on what parts make up the system and what generally goes wrong…

System Components and Typical Failure Characteristics:

Listed more or less in order of declining likelihood of faults...

Springs aka 'bags':

Rubber airbag springs at each rear corner. Sooner or later they WILL wear out. Will typically start to leak erratically and rarely at first, then eventually becoming more and more frequent until at some point may be total failure to pump up. At first car will sit low from being parked overnight but then 'pump up'when a door is opened. When truly begin to fail will throw dash SLS failure error as pump has to run all the time to keep them pumped, but when they are slow leaking there will be no codes. Extreme failure of one bag may result in both sides going flat / low as the module can no longer pump up one side so it will match the other side to that ride height.

Bags seem good for 100k mis + / 15yrs sometimes but sooner or later…

Easy to replace and not expensive comparably (to many OEM airbag systems). OEM bags are available. Arnott's are available aftermarket using Contitech air bladders that seem to be very good. There are also some Chinese no-name parts that do not get good reviews.

Difference between Sport and Regular bags is unclear but there are 2 versions indeed from the dealer. Aftermarket does not offer 2 versions. I would be nice to be able to document the difference between the 2 parts, if there is any...

Ride height sensors:

One located on each rear suspension corner with lever attachments to the body, and corresponding electrical connectors. Levers can get borked up with dirt and/or corrosion. Connectors / wiring can get borked up. Don't tend to fail that often on their own from wear/age, seems more usually it's that they’ve been whacked / abused. Can be read in INPA to check for proper operation & viable signals. May throw SLS codes if the module can recognize that they aren't working, or may not.

Sometimes fixable in-place, but if not replacement of connectors and/or lever connecting arm parts and/or sensor is the route.

Air lines:

There are 2 types of lines.

1. Small plastic lines that go to each pair of bag+reservoir, coded red or blue for each side. These supply the air from the pump assembly to each corner.
2. larger plastic tubes with clips on them that are the connection between each bag and its reservoir at each corner.

Lines in general are almost impossible to fail on their own, however poor mechanics, or some freak pinch of something under the cargo could cause an issue.

If the smaller red/blue lines are cut or damaged, there are small 4mm push-on splices available that should work to be able to rejoin a damaged section and/or even splice in a new piece of line. Any high pressure 4mm pneumatic line should be fine for replacement and the red/blue thing is an industry standard so even replacing full lines should be possible with non-OEM parts.

As for the bigger black reservoir tubes, clips for the reservoir lines are fragile and reported to break, poor mechanic service can damage these. This is a little more of a problem, as they are officially 'part of the reservoir assembly'.

Reservoirs:

Big metal tanks that bolt up from underneath the car. These are indeed bit of PITA to get out. However the only thing to fail on them is really the plastic hose / clip part, or, in extreme use conditions, for them to rust out. Fitting clip damage is unfortunately not uncommon, the official repair is full replacement of the reservoir assembly, although one can probably fabricate a fix for the clip if one is clever. They do not tend to rust out commonly unless car has been subjected to some truly extreme conditions, although moisture build up in the system could be a contributing factor.

Pump assembly:

This includes the pump and the series of solenoid valves that manages the air to the bags and reservoirs. Located under the "UFO dome" under the spare tire. It is a complex single-assembly supplied to BMW by Wabco. The assembly is also now available in the aftermarket from Wabco via Arnott.

The important sub-components are..

(1) air pump
(3) solenoid valves
(2) check (one-way) valves
(1) air pressure 'maintenance' (regulator) valve
(1) relay
(1) air drier (dessicant)

The pump assembly seldom just fails on its own, true failures more only in cases of spare tire well flooding. Many reports of incompetent shops blindly declaring "bad pump / valves!" making owners shell out for whole assembly and having that not fix the problem whatsoever, leading owners to conclude the SLS system is terrible horrible unreliable and expensive when in fact its their mechanic that's horrible terrible unreliable and expensive. In addition, the module may throw codes if it detects that a portion of the pump assembly is shorted or not operating properly, although it is limited in what it can diagnose, and if leaks are occurring and are from the pump assembly the module won't be able to discern this.

Diagram below shows sub-components of the assembly. Individual parts (i.e. solenoids etc.) are not officially available although some industrial parts may well be possible to find with resourcefulness.

Someplace there was a post or thread on someone who'd found some solenoids that dropped in I believe but I can't seem to find the thread at the moment. Forum member adm750 documented how to remove the solenoids to replace o-ring seals and inspect and lubricate internals (below). If solenoids are sticking and/or leaking at O-ring seals then that should be easily serviceable. If solenoid piston face rubber seals are eroding, or the solenoid coil is burned out, then new solenoid parts are going to be required.

If the pump itself is starting to fail, there's a dude who offers some kits for rebuilding the E53 compressors, it seems it also would apply to E39's but should be confirmed http://www.bagpipingandy.com/
E53 guys also seem to report using this kit to rebuild the pump as its the same as used in some Porsches, MB and Audis: https://www.ecstuning.com/b-genuine-...it/100698010a/

According to this MB thread using a different but similar Wabco pump, if the system is water logged the drier can be opened up and the silicagel beads dried out to restore them. If one is messing w/ the module at all, drying out the dessicant would probably be an advisable procedure to add to your list.
http://www.benzworld.org/forums/7931225-post15.html

SLS Module:

Brains of the system, sits on the inside wall of the tire well right on the other side of the battery. Should be able to connect with INPA or suitable BMW-compatible scan tool or software, and read status/codes from the module. Not much to be done if its not responding or reporting logic errors or behaving erratically except replace with a new or used part. But again - very very rare to just fail on its own without physical damage.

SLS documentation:

Full documentation on the system operation and components. Most mechs don't seem to have ever seen anything like this unfortunately:
http://www.e38.org/selflevel.pdf

Key extracted pages from that document...

Overall system component & location diagram:



Module & pump assembly control system schematic showing inputs and outputs:

[jay525]

So to follow up on my situation. Raised the car, all the bags are rock solid, no holes. Put it back down, rear is sitting higher then the front right now. Mechanic is out driving it right now to see if it lowers. Just saw him take a bump, rear looks low to me....will update you shortly.

[dohalloran]

Wow. Great post there GG. Love reading how "stuff works" and what can go wrong. I know my bags were replaced once, not too long ago. Everything works as it should right now. Appreciate you doing that write up !!

[jay525]

Bags still holding. With all the issues the bags gave me last night I assumed they'd be able to find the issue today. He's out driving it around again in hopes that when he parks it it will lower. Amazing....
Based on this post I'm leaning towards having him replace the airbag even though he can't find the leak and says its rock solid.

[jp5Touring]

Very informative,nicely done.

[geargrinder]

Bags still holding. With all the issues the bags gave me last night I assumed they'd be able to find the issue today. He's out driving it around again in hopes that when he parks it it will lower. Amazing....
Based on this post I'm leaning towards having him replace the airbag even though he can't find the leak and says its rock solid.

Force your mechanic at gunpoint to read the PDF.

Does he have proper scanner to check the module? Check sensor signals?

[jay525]

He checked the module, nothing. Right side lowered after I made it home, ordered the arnott springs, he's putting them on next Tuesday, both sides. I mean they're 15 years old I'm sure they need replaced, just curious if I should replace anything else while he's at it.

[geargrinder]

Yeah "checked the module" sounds like just scanned for codes. If he has a good scanner he could read the height sensor values and see if they say something funny. In fact you could have the scanner online and have someone move the sensor (on the lift w/ the link disconnected) and see if it reads continuously or erratically...

But... indeed you'd need bags sooner or later so, even though its a little "parts shotgun", its not a terrible way to go. Have him clean the electrical connectors and physical levers / links for the sensors while he's under there.

[jay525]

I'll definitely have him clean it while he's under there, and I'll update everyone afterwords. Obviously this is a fairly common problem...and people run into the same situation as me, mechanics not wanting to fix something they can't verify is broken. So if my problem is fixed hopefully it encourages more people to just replace the bags at this point instead of when it gets worse.

Car stayed up overnight, but it's definitely lower then normal...and continues to get lower. The "finger test" used to let me stick 4 fingers on the right side, now I can only get two fingers in. Great for a relationship, bad for a bimmer.

[geargrinder]

LOL. where's manny. One test is the good old standby - spraying soapy water on the bags and looking for bubbles. That counts on a continuous and notable leak though. IF its pinholes that only leak super slowly... no gouda.

[jay525]

My guess in pinholes. The airbags need replaced for sure, and I'm fairly confident that will solve the issue....I just don't know if there's anything else I should have him do while it's all apart.

[jay525]

Bags arrive today. Car sat 48 hours and finally lowered last night. Put the money on pinhole leaks and hit vegas gg, I think you nailed it.

[juststeve]

I just don't know if there's anything else I should have him do while it's all apart.

A new pump cyl. seal can be had from ebay for under $20. Fairly easy to install using minimal brain cells.

[jay525]

A new pump cyl. seal can be had from ebay for under $20. Fairly easy to install using minimal brain cells.

These are getting installed soon, I assume I can have him grab the kit from the dealer?

[geargrinder]

Nope. Dealer answer is buy the whole pump assembly for a billion dollars.

[jay525]

Damnit man,i knew you'd sneak back in here and give me bad news. Any chain store sell a generic pack that should have them in stock? Or other suggestions on getting them this weekend?

[geargrinder]

First of all friend, you've turned this into your own problem thread. Honestly in cases like this proper forum ettiquette is to make your own "This is what is wrong with my car" thread. Its how the system works, I think I told you that when you were just piggybacking on the other guys thread before, now you're threadjacking this one. So go do that please. One or two posts is fine but you've now jacked this one up pretty good.

Pump rebuild? To be honest I wouldn't sweat it so much unless your pump is showing signs of crapping out. Doing the pump work has little to no overlap w/ the bag labor except taking out the rear cargo floor and the spare tire, and in fact for doing the bags the spare tire doesn't even have to come out. If the pump seems to be not holding up you can always do it later. This is a weirdo hobbyist DIY part it seems so you're unlikely to stumble on it at AutoZone or O'Reilly's or whatever. No affiliation but I googled on juststeve's suggestion and here's an eBay auction that ships from US (a lot of them seem to be overseas...) basically they seem to be knocking off the bagpipingandy kit at a big discount. Whether parts are identical or lower grade is unknown.
http://www.ebay.com/itm/RANGE-ROVER-...-/182046213757

Now:

To be honest I'm re-reading your latest updates. The car has been sitting TOO HIGH and won't come DOWN? Then the bags are fine and the pump is fine.

Thoughts:

• Overall - Your mechanic indeed seems incompetent on this. Did you make him read the PDF at gunpoint as instructed, or did you skip that step? He almost certainly doesn't have a proper scanner that can read the sensor heights otherwise he'd have more information and ideas than "DURRR I DUNNO MAYBE NOW WE CHANGE THEM BAGS ANYWAY". He'd be able to read the sensors and test them and say "yes they seem to be reading correctly and responding correctly".
• Possibility 1 - the rear ride height sensors are jammed / borked / physically-disconnected
• Possibility 2 - somebody (the mechanic) tried to recode the module for higher ride height to make up for the sagging due to some pinhole slow leaks. I should maybe include this in the write-up. It is not uncommon stupid thing for only-half-capable mechanics to do. so if he's recoded the module to try to 'make up for the sagging', the car will now pump up super high and try to maintain that ride height.
• Possibility 3 - super long shot here, extremely unlikely - there's a jammed solenoid making the system go over pressure. it's not this, trust me, its 1 or 2 that are the problem.

Now go start your own thread and we'll all move over there.

[jay525]

I sincerely apologize for thread jacking and offending you. My comment was truly meant as a joke, and I do respect your knowledge.

[geargrinder]

Oh I'm not offended - just hit tipping point really . Still want to help solve your problem.

[lilflipM42]

Great post!


Sent from my iPhone using Tapatalk

[geargrinder]

Solenoid disassembly and cleaning...

This is a shot of the connectors...and he small metal locking clip in the position where they can be removed (like anyone needed that picture...but here it is)
Attachment 590484


This is one of those valves removed. Just loosen the two screws evenly. If the assembly is in the car and there is air in the system, it will try to escape while removing the valve so make sure you don't just run these screws out quickly. Slow and even.... Once the screws are out, the solenoid slides straight out.
Attachment 590485


This is of the solenoid expanded...with the piston and the spring removed. The o-ring can be taken off, cleaned and lubricated. I used Parker O-lube on it, and the surface inside the solenoid where the o-ring makes contact. O-lube is pretty tenacious stuff so use it sparingly. I rubbed some O-lube on the face of that piston. That is soft rubber and makes contact with the port in the valve body. I also put a dab of 3-1 oil on my fingers (the ones w/o the O-lube on them...haha) and rubbed the piston itself just to coat it and protect against moisture damage. I did that to the solenoid body too. Since my pump was akin to a fish tank bubbler when I first bought the car, you can see the white corrosion on a lot of surfaces still.


Attachment 590486

[DiscoContented]

I know I'm resurrecting a very old thread and I apologize in advance for that. I've tried posting my question but it never seems to show up.

2010 F07 550i GT XDrive. Single EHC.

I have replaced the compressor, relay, ride height sensors on both sides, and valve block.

The compressor can be run when I jump power directly from the battery. Fuses are good. Relay clicks when power is applied.

The wiring harness shows signs of corrosion (green scale because it's brass) and there was water in my trunk below the spare.

I've tried raising the ride height and activating the compressor using ISTA and ENET. I have input the new ride height settings in order to calibrate. No joy.

Is it possible the EHC was shorted? Any tests I can run or would I just throw in a used EHC?

Any help would be greatly appreciated!

Thanks!
Erik

[geargrinder]

I know I'm resurrecting a very old thread and I apologize in advance for that. I've tried posting my question but it never seems to show up.

2010 F07 550i GT XDrive. Single EHC.

This forum: E39

Your car: F07

My advice: either...
1. Sell car. Buy used E39. Find out what problems it has. Post questions here.
OR
2. Learn to internet.

[ca2002mp2]

I'll drop this off since OP was so nice.. I did my run with the airsprings and found out something really interesting that is NO WARE on the web and here for the first time. for issues with slow leek, mine was in the valving system which is a common area.. try to find it and you wont... BUT I solve mine with a 2.00 bike tube fix kit.. it seems that the piston that moves from solenoid activation has two rubber tips on each end that seal off the system from the pump side to the bag side. When the tips ware out (ie the rubber hardens) air leaks.. solution cut an ever small piece of the tube patch and put that on top of the piston on each end. That fixed mine..

[geargrinder]

So you're talking about homebrew solution for the type of failure I mention here:

If solenoid piston face rubber seals are eroding, or the solenoid coil is burned out, then new solenoid parts are going to be required.

Cool. I still bet you the solenoids are available through either secret undiscovered parts-crossover or via industrial solenoid sources, and that's how I'd probably go if I had that problem, but nothing wrong with a little homebrew improvisation.

- - - Updated - - -

Honestly I'd forgotten I wrote this thread... Probably should be pointing people at it more often when they ask questions about SLS or come to dumbass solutions...