The Airmatic on my 2011 E550 is stuck in sport. I plugged in the scanner, and got the following:

Digging a little deeper, it tells me which corner, which is nice.

Digging deeper still, I'm able to actuate each strut independently. The remaining three corners turn on and off with the expected current draw. Left front will not actuate, and shows a constant current draw of 7.8mA. That checks out with the rest of the scanner output.

A month or two ago, I replaced the driver front half shaft. This involved unplugging the harness at the strut. This fault appeared more recently by at least half, but it's a datapoint that may not be nothing. I unplugged it, blew out any dust, and plugged it back in. No change. I attempted to trace the harness back into the vehicle, but I only had time to figure out where it passes through into the engine compartment.

Where else can I go about looking for things, and what else can I do to track down the source of the issue? TIA

 

Your investigation validates the strut reported as "defective" after beeing disconnected for an axle swap.

Let's try to understand how this may be a false fault.
Like computer denormalized strut position after seeing open circuit...

The harness seemingly provides the super-small 8mA current: good that it is not "open loop": ok!
How many wires in this connection: 2 or 4 (pwr + ctl)??

There are not many things that can be attempted:
-A- you have tried "actuation tests": failed.

-B- I am sure you've tried "clearing fault"

-C- How about "normalizing" or "retraining" new position?

> Do you have a "position sensors" reporting height or your strut does that all by itself?
🤞

 

This is for the magnetorheological aspect of the shock absorber, not anything related to the air part of the Airmatic system. The sport/comfort switch controls ride height as well as damping firmness. Position is irrelevant, and all of that seems to be working and reading as intended. It'll still raise and correct for load changes, etc.

Additional info:
-The plug going to the struts have two leads. Just on/off voltage to align/relax the ferromagnetic bits in the shock fluid.
-When the other struts are OFF, there is 0ma going through them. I forget how much current when they're on, but I recall it was substantially more than 7ma.
-The strut is only about a year old.

 

Thinking about it further from a purely electrical perspective (without any consideration for black box software), I can rule out or confirm a short in the shock itself by unplugging the strut and checking to see if it's still pulling 7.8mA. Unplugged, there would be no way for any short to occur if it's downstream of said plug. If it still occurs (again, ignoring any software considerations), that tells me it's upstream of the same plug. Similarly, if I can trace that lead back to wherever it goes, I can unplug whatever wire, and once the short goes away, I've figured out where the short is. I doubt there's much between the strut and the control box, but maybe there's a plug that goes into a bus cable or something... Anyone have any thoughts on this?

 

@S-Prihadi @konigstiger or any other especially knowledgable type? The lack of responses or search results tells me this is one of the deeper rabbit hole sort of issues. Is my strategy for somewhat manual troubleshooting valid? I'm a pro with classics, but the high tech stuff is pretty new to me still.

 

I just got back in country.
I will look up the wiring diagram for ur suspension, since the scanner shows the VIN.
Shall see what we can find.

Usually MB computers send low power to solenoids as diagnostic means.
It will take more than 7.8 milliamps to actuate any solenoid.
Best you see what is the actual value when other dampers are activated and trick the left front wire to get the same load using small bulb or resistor to see if
damper ECU and wiring is OK and the damper solenoid is the issue.

I have no experience with such adjustable damper, need to know its actuation or de-actuation protocol : is it a momentary signal for X seconds or a permanent signal/power like
normally a typical solenoid woud need ?

 

Your suspension is code 489
I think the command/signal could be a flip type.
Say NORTH oriented magnetism or SOUTH.... using momentary signal where DC polarity flip can be done and NORTH/SOUTH magnetism can be flipped too.



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..




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Try to test a good side damper for this flip signal.
You may need to rig a jumper wire because damper controller may not send out signal if in open circuit mode ( connector unplug totally ), while at it use DMM ammeter function
and confirm true amperage demand.

.

 

I'll have to check the specific amperage fed to the working corners. As I recall, it's constant, which makes sense since it's activating the magnets to align the ferrous bits in the shock fluid. I'll verify this though, and get numbers.

Ok... Either, there's just a plug at the shock (X62/7 in the diagrams), and then a plug at...? 3? Is that a black box with computers in it? Some arbitrarily convenient access point for the CANbus? (Pardon my ignorance, this is my first car of this recent a vintage that I've had to do more than basic maintenance on AND my first Mercedes.) Or is the notation here such that there is a plug at the shock (Y51), another at some interstitial point X62/7 (where/what is this exactly?), and then another at 3? It sorta makes sense that there might be an additional junction in there since the wire connecting to the shock is in a vulnerable location in the wheel well. Would help with serviceability to be able to replace a short and easily accessible pigtail rather than a whole harness if something got stuffed. Are there any diagrams in your software for the physical location (and maybe even appearance) of things?

I'll poke around this weekend if I can manage the time. We had a major wildfire last year (national news level event), and there is a mitigation event this weekend that I'm assisting with. It's only supposed to take a day, but I've seen what we're up against, and that ain't gonna happen. Not sure if the balance will be dealt with Sunday or at some later date... I'll be out of town for the following three weekends, so it could take some time, unfortunately...

 

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The X62/7 is an intermediate connector and of 4 pins.



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]



Get ebay version WIS/EPC, up to 2020 is good enough.
Without it, you can't work on MB cars properly and professionaly albeit DIY.

Good luck......

 

I miss print manuals... You're probably right. Doesn't look too expensive. The need to spin up a PC laptop and find a working optical drive are the bigger hurdles. I was hoping to get by with the shop scanner, but the information on that second page (all of them really) is a huge time saver.

 

Some sell those WIS/EPC using download link I think.
So no need CD ROM drive.

Mine was from CD ROM drive back in 2018/2019.
My version is 2018 EPC/WIS but I managed to get WIS only 2020 version.

 

Finally getting around to this... I've been using what I think is an online version of the same manual, and it seems to be giving me all the right and same information for the most part. Time to test the theory... I've poked around a bit with a few things now that I hadn't in the past... ugh... 7 months...

With everything fully assembled, I get the constant 7.8mA draw. So I unplugged the strut to see if the draw went away (indicating the short is in the strut), and it didn't. I tried shorting it at the plug to see if it changed anything, and it didn't. So I moved up the ladder a rung, and unplugged the pigtail where it attaches at the firewall (indicating the short is in that bit of wiring). Also no dice. Still indicating 7.8mA draw across a short.

So now I'm at a bit of a conundrum... The wiring on the inside of the engine bay seems to go straight into the main harness, so I'm not sure I'll be able to do much there.

Looking at the diagram here (which is essentially the same as the system output above, but with handy color coded wires like I'm used to), it reads like that goes directly to the Airmatic control module under the right side dash... I'm delighted to see that it appears to be a single pair of wires going directly to that module, and not just feeding into a CANBus harness to disappear. I'm not 100% sure that necessarily helps me all that much though...

After all of that and a few other things, I came inside and got cleaned up so I could investigate a bit and take care of some work stuff that cropped up while I was trying to take advantage of the lull. I think my next step is to dig out that module, and hope that the wires going into the plug are such that I can see the wire color coding and probe a bit. Either it's in the harness, and I'm probably screwed, or its in the module, which I haven't investigated yet...

Any bits of wisdom at this point?

Edit: Continuing to investigate, and I just discovered something interesting... I had another code at some point related to the navigation system (which I don't use, and thus wasn't all that interested in messing with), and I just discovered it's in the same general location as the airmatic control module... I wonder if there might not be something shared there...

 

OK. A bit of time and cooperative weather today. I studied the electrical diagram thoroughly. I identified where the suspension control unit is, identified which plug the shorting strut is on, and finally identified everything else on that plug as being direct end-point sensors. That means, I'm quite sure, it would be OK to have that unplugged with the module getting power, and that it WOULD get power.

First things first, we're talking about a short. That means somewhere there's continuity between ground and something that's not supposed to talk to ground. I pulled the plug, identified the pins in question, and found some jumper wires with the right size to fit the plug. I put them in the two holes for the strut, and checked each for continuity to ground and each other. Bupkis. Just to be sure, I found another wire that's supposed to go to ground, and confirmed that it read accordingly. Cool.

Then I hooked the battery back up, hooked up the scanner, turned the car on, and checked the live data on that same strut that's supposed to be shorted. Sure enough, it's STILL reading 7.8mA! That's with the strut in question not connected to the module at all! Ergo, the issue is in the suspension control unit.

Problem diagnosed. I need a new control unit. I looked into them briefly a day or two ago, and they're not super expensive, but I need to make certain that it's plug and play. BMW would require pirated software to register the module to the VIN and blah blah hostile to customers blah, but it doesn't seem that's necessary here. What is necessary is a calibration of the module to the car's struts and sensors, and that seems a bit fraught and perilous...

I read up on that, and a lot of people have trouble getting the module to accept a fully completed calibration routine. There's also a big giant and seemingly universal question mark surrounding inclination inputs. I believe I have an appropriate tool to get the correct reading IF I can figure out where it's actually supposed to go. So far, I've not found that bit of information. Also, if it gives me the opportunity to lower it a bit while I'm at it... That seems like a fun little bonus. I think though, this more or less concludes the subject matter described in the thread title, and is moving into new territory such that if I need further assistance, it'll be helpful and most appropriate to start a new thread with a more applicable title.

So, barring any questions or anything, hopefully if anyone comes along behind me with this same code, I've been detailed enough that what I did to diagnose the issue that caused it is clear. I will be around if there are any questions or comments.

 

Finally got around to this, and I'm pretty frustrated.

To recap, the computer sees something like a 7mA current draw in the left front strut. Nothing precipitated the condition that I'm aware of, just went into sport mode one day and wouldn't come out.

I unplugged the strut, and it still sees the current draw. I unplugged the strut pigtail at the wheel well intrusion, and it still sees the current draw. Looking at the electrical schematics, from there it goes straight to the active suspension computer. I unplugged the harness there at the computer, and it STILL saw the current draw. From that, I figured the short had to be right there within the suspension computer.

I replaced the suspension computer just now, got everything calibrated and happy, and... IT STILL SEES THE SHORT! If it's not the strut, not the harness from the strut to the computer, and not the computer... what? Does that mean it's something upstream via the CAN bus?

That would imply one of the following:
- Instrument cluster, don't see that having much to do with struts in a way that a short would manifest like I'm seeing it.
- ME-SFI [ME] control unit (engine computer), same as above.
- Front SAM control unit with fuse and relay module... Maybe, but it's connected via 4 wires, and I kinda doubt one of those is dedicated just to a single strut.
-- further upstream of the Front SAM control unit is the rear equivalent
- One of the following
-- Electronic Stability Program control unit, possibly, save that it seems mostly related to just brakes.
-- Regenerative braking system control unit, nope
-- Premium Electronic Stability Program control unit, this seems to be related to advanced safety features like radar stuff that I don't have

Does anyone have any ideas or suggestions for next diagnostic steps here?

 

Beware the DTC definition of SHORT is really confusing.

The suspension module reports a short because the circuit is missing one side... either the (+) or (-) side.

Meaning the circuit reports as SHORT is an OPEN circuit that's not switching voltage. It appears stuck as if shorted out...

Hope this can help your progress.


I duno these smart suspensions... if you can summarize issues & tests perhaps we can focus on solutions.
I custom ordered my car with these ferromagnetic suspensions but the resulting build only basics dampeners.

 

Cali is right, DTC saying SHORT could also be OPEN circuit.

Also sometimes there is what we call SUBTITUTED value. Where when certain sensor is un-plugged, the control module knows and place a fix programmed value as subtituted value.

Here is an example where I seen subtituted value in action, for my GDI fuel rail pressure and temperature : https://mbworld.org/forums/e-class-w...re-sensor.html


Wheel speed sensor also get subtituted value, when wheel speed sensor connector disconnected or if sensor defective.
https://mbworld.org/forums/e-class-w...ml#post8958990

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For certain sensors or devices, when it get unplugged, if I recalled is my friend W204 oldie halogen 5 watts parking light for front headlight, the Front or Rear SAM will declare DTC and shut off
the power to the bulb and when you test with a multimeter, it is dead wire. You must install a healthy bulb first and then re-measure the voltage, here the Front or Rear SAM senses the PROPER load is back,
and it will then apply power to the wire set.

 

Back on 18th July 2025 I asked this : Post #6
It will take more than 7.8 milliamps to actuate any solenoid.
Best you see what is the actual value when other dampers are activated and trick the left front wire to get the same load using small bulb or resistor to see if
damper ECU and wiring is OK and the damper solenoid is the issue.

I have no experience with such adjustable damper, need to know its actuation or de-actuation protocol : is it a momentary signal for X seconds or a permanent signal/power like
normally a typical solenoid woud need ?

My post #7
Try to test a good side damper for this flip signal.
You may need to rig a jumper wire because damper controller may not send out signal if in open circuit mode ( connector unplug totally ), while at it use DMM ammeter function
and confirm true amperage demand

=========

I am repeating again........
Do real live test, using DMM milliamps.
Is it really 7-8 milliamps of current draw on HEALTY struts and the suspect strut, when all wire harness connected ?
You have to work on KNOWN good side first, in order to verify the PROBLEM side.
Don't trust your scanner too much, more so when it is not Xentry. Even Xentry sometimes color red some values, causing us to think RED = No Good, but actually it is OK.

Autel can't even name the damper controller unit properly, Autel call it VC04 - Left Front axle damping valve unit.
MB wiring call it Left front axle damping valve unit (Y51) , probably Xentry will call it Y51 too. Yes sometime Xentry may call some component by its older name 1 generation ago.
But what I seen on 3rd party scanner, the name they call devices could be two generations ago. Launch has more up to date naming of devices, usually, compared to Autel, if for my W212.


Second option is you raising the white flag and send it to an MB expert workshop.

 

I did most of that, just didn't make it to the thread. Apologies.

The actuation voltage is much higher. Hundreds of mA from memory. Not even close to 7.8mA. It's held as well, not momentary. Low (0mA) is apparently sport mode, and High is comfort mode.

If the 7.8mA is a holding value that it's showing due to an open circuit, or the named short, then I should be able to replicate it on the known good side. Unplug the strut at the strut, and it'll either give me 7.8mA or something else. If it gives me something else, jumper (short) and see if THAT gives me the 7.8mA reading. If the former (open) gives me 7.8mA, it checks out with the other side. If the latter (the actual short) gives me 7.8mA, then I still have a pretty significant problem, because unplugging all the way to the computer and then changing the computer gives me the same short.

The counter to this theory is that when I ran the short back to the computer, in order to unplug the offending strut, I had to unplug everything; all the struts plus a handful of other sensors. I got clean 0s across the board except for the same circuit. That's essentially the same as the first half of the above. Only, removing the supposedly shorted strut didn't change anything...

 

OK, your second N51/3 Module which you call as : suspension computer .....is new............. or is it pre-owned unit ?
Low probability but even new module can go bad, but to be bad at the same Y51 Left Front Damper Valve section is probably rare...we never know.


Is this the module in your car ? Sorry man, got to ask.... mine is dumb passive suspension type

.
Above video seems the correct module in reference to wiring diag 489 v1 I posted.
3 connectors into the N51/3. No #1 is longest/biggest one of 48 or so pins. No #2 is approx 30 pins. No #3 is only 2 pins, CAN BUS E.
Your supposedly faulty Y51 Left Front Damper Valve unit so happened to be at connector no #2.
The Y52 Right Front Damper Valve unit also at connector no #2.

One last try.
Wire the Y51 and Y52 criss cross. Use extension wire or jumper, up to you.
Reset/calibrate the system after wiring criss cross.
See if now the issue goes to Right Front or how ?

There was a GLE400 which its air-conditioner when the compressor got replaced, we need to tell the module ( using Xentry ) that this is a new compressor being installed and
the the module re-learn....and only then the HVAC return to normal.
ODD and WEIRD for me, because my W212 does not need me to do so, when I removed my compressor to do oil balance and replace o-rings and replace 3 hoses as preventive...I did not replace the compressor but I emptied the R134A.
I mean there are certain steps we non-MB trained dudes may not know.

 

It appears to be rebuilt. Came from Mercedes. The odds of two being bad in the exact same way, seem nil. The new one has a "passed" stamp on it, which suggests at least some manner of testing, and an internal short would be hard to miss.

That is the unit. N51/3. Correct, all the incoming sensors are on connector 2.

You have to recalibrate the airmatic when replacing the computer. I did that successfully. Still has the issue.

I'll have to go study the wiring diagrams a little more closely. I believe I have jumper wires that fit in my electronics shop to try swapping sensors around. It's going to be a massive PITA, but this ghost short has been a massive PITA all along.