Ultrakla$$ic

I went out to move the car out of the garage after putting the rear wheels back on and I let one side of the car down off the floor jack, walked around to the other side, let that side down and proceeded to start the car. Moved it out of the garage and drove it maybe 50 feet and the dash lit up with the AIRMATIC MALFUNCTION message. The rear of the car was all the way down, but the front was still aired up. I guess my rear height sensor died. My car is a 2012 s550 W/O 4-matic and W/O ABC.........so I only see one rear ride height sensor correct? Searching the net some mention 2 sensors in the rear but I only see one on the rear drivers side???

Any and all feedback would be greatly appreciated.

Ultrakla$$ic

Would anybody have the part number to the rear ride height sensor for my 2012 w221 s550? I can't seem to find a definitive part number for my model year. FCP Euro doesn't seem to list one unless I'm missing something.

Arrie

Did you do a restart on the car?

BOTUS

likely u snapped off the rear height sensor - its normal - its a nightmare to fit... use a worm drive hose clamp to retain the new part - you will never be able to clip itself back together (don't even try you'll trash the bracket and get nowhere)

look with a bright torch - in front the the left rear wheel (at axle height) in towards the anti-roll bar you should see the link dangling - using the worm drive hose clamp you may be able to reattach (temporarily) the snapped of bit - with the wheel off, car on the ground, but its not much fun

Ultrakla$$ic

Thanks Arrie

I did, and also ran some code checks and Live data

Thanks BOTUS,
I checked the sensor and retaining mechanism and all seem intact. However, here are some code checks and Live stream data I find interesting. In the pic with the voltage to the Left and Right Front Level sensors (2.67V and 2.41V) seem adequate, however the voltage shown from the REAR level sensor is only 0.51V so is my REAR level sensor dead or weak or malfunctioning?? Also, I'm assuming this defunct rear level sensors inadequate voltage signal will shut the compressor off as shown in the pic as a safety measure as noted by the Data pic "Compressor Locked Due To On-board Vehicle Network Emergency Mode"????

PICS:



(PIC ABOVE) REAR AXLE LEVEL SENSOR VOLTAGE INSUFFICIENT?????





(PIC ABOVE) COMPRESSOR LOCKED DUE TO INSUFFICIENT VOLTAGE FROM REAR LEVEL SENSOR????





I appreciate all input guys.

BOTUS

locked is an interesting one - mine had that, I couldn't get it to clear (at the time with an older simpler tool), I have never confirmed what causes or fixes it.

with the stupid uninformative "locked" message and my tool not saying how to fix.... I went to a local Merc specialist - maybe using dealer tools they did something in diagnostic tools - within 3 mins of me arriving they had the compressor running - but they did later say the fuse was popped Front SAM (big orange 40 amp one) - I now suspect it had just popped - but can't confirm

not seen any volt readings using the kit I have - but whats it say for the rear ride height ? the front being a bit different seems familiar - but the rear should have something similar - r u sure the rod isn't just dangling ? I think until the reading from ALL the sensors are realistic it MAY remain locked

Arrie

Those voltages say “signal” that to me would mean the signal that comes out from the sensors and changes with the car level.

In your first post you mention you put rear wheels back on and then lowered the rear down. Does this mean the rear wheel hubs were “hanging” in the air free? In this case the Airmatic lets air out from springs as the free hanging hubs will lower as they don’t touch ground via wheels. The Airmatic thinks the rear of the car is way high. When you then put wheels on and let car down on floor it went all the way down as there was no air in springs to hold car up at all.

Now an interesting question is if the system has this limit build in the system that if level is below some minimum value it locks out the compressor? That is what it seems by your scanner.

You might be able to bring it back to life if you jack the car up some to bring the signal from the rear sensor up above the low limit that we don’t know what it is. Could be enough to jack just one side as they both move the one sensor. Better if you have two jacks. Do not raise it above normal level as this would keep compressor down.

This could get it going again unless it takes xentry or some better scanner to remove that compressor lock. Perhaps disconnecting the battery for a few minutes would do it…?

Ultrakla$$ic

Thanks continually for the help guys! BOTUS, I do need to check the fuse under the passenger side floor mat SAM module and thanks for sharing which one it is, The rod is indeed intact an attached correctly. Going to check the fuse later today.

Arrie, thanks to you as well. Interestingly enough I just watched a video regarding voltage changes while viewing LIVE DATA STREAM in my Scanner and I put the rear on 2 floor jacks and lifted the car to "normal height" and the "REAR AXLE SENSOR VOLTAGE" stayed at 0.51V while the 2 front level sensor voltages fluctuated on the screen even though the jacks were in the rear. According to the video I watched, if the REAR level sensor is "working" the voltage should fluctuate as the height changes but the rear voltage stayed at 0.51V.......interesting.........The Live Data was able to reflect the voltage changes on the front sensors since there was SOME change in height of the car overall. Interesting. I need to check the hoses going into the valve block as well to make sure they are secure and pushed in all the way as well as no leaks at this point as well..........however, with my pump being "locked out" leaks are going to be impossible to find.

Game Plan:
Check Valve block to assure all air lines are pushed in all the way
Check SAM fuse

Keep the suggestions coming guys, it really keeps me focused and helps a ton.

Arrie

If the sensor output does not change with changing car level then either the sensor dies not move with level or sensor is bad.

Electrical connections should be fine as you don’t have an error for that.

BOTUS

the F SAM is under the bonnet - not inside, with 4 x 8mm headed bolts on the black box of fun near the brake master cyl

BOTUS

when I say big fuse - that's as in physically gigantic - a 40 amp orange fuse and the only one in there - you can use a 30 amp "to try" if that's all you have

Ultrakla$$ic

Oh okay, I checked that one yesterday! All good on that one! Strange thing I've discovered is when you buy a new Compressor pump, they give/recommend you change the RELAY in the fuse box???? Wonder if the RELAY is cooked/broken???

Arrie

Did you not read my previous message? If the sensor output does not change with car level change you either have a bad level sensor or the sensor does not turn by the linkage when level changes.

BOTUS

yep - new relay whenever you fit a pump.... I guess they burn out - or stick on

BenzNinja

iTrader: (4)

good tools, fast and good repairs

Ultrakla$$ic

Sorry Arrie, I was trying to reply while driving and stopped at a redlight. I did see this and I'm sooooo appreciative of all you guys input. I hope it's just a bad level sensor like you've revealed. Gonna call FCP Euro tomorrow to see if they have these because I can't find them on the site.

Interesting. Thanks BOTUS for the input along with Arrie!

So in theory, the level sensors are likened to potentiometers that send a signal to the ECU to turn the air compressor on and this triggers the airbags to fill or air out. The higher the voltage sent from the level sensor the higher the car lifts upwards and vice versa. When there is a problem with this system, the air compressor just stops working to prevent any movement of the air ride therefore causing the owner to cease driving the car and fix the problem??

Did I miss anything??? Question, what would happen if there was an AIR LEAK in the hoses or airbags? Would the compressor be signaled to "shut off indefinitely" until the leak is fixed or would the compressor try to run until it figured out that the car wasn't rising or falling and time out and do this over and over, but at least one would be able to rule out a broken air compressor right because in MY CURRENT situation, the compressor does not kick on at all????

BOTUS

the plastic part of link rods seize on the ball joints - usually around 5 to 8 years where using some magic Merc invented - the plastic welds on with enough strength to over come what you can do with vice grips - then the little spring steel legs snap off bit by bit and you get around 12 months where it seems to cope with loads as these steel bits bend and snap instead - often giving weird ride heights in each corner at random intervals - these then settle with the right type of bumps and driving

if you get unlucky some retard gets at the car with dealer tool and resets the correct factory settings (than never go wrong) - with new junk ones trying to suit bending variable linkage readings

eventually the pump gets lazy, the bags probably weep a bit of air and the seized link rods mean the car is a muddle up

Ultrakla$$ic

Dumb question but when changing the rear height level sensor should I disconnect the battery before doing so and if so, remove positive or negative cable??? I shouldn't expect any ill side effects in disconnecting the battery because its a Mercedes right??

BOTUS

no need - but you will struggle like hell to reach it without a ramp - and even then its an utter nightmare - some moron put the park brake module directly beneath it - when the obvious thing was to have on one side, and the other part on the opposite side of the diff - but that would have taken thought, consideration and a little bit of nous - of which Mercedes Benz has none !!!

Ultrakla$$ic

indeed you speak the truth my friend!!!! I got the rear height sensor bracket and all connectors undone but like you mentioned not before I lost half the circulating blood in my body from the cuts, scrapes and gouges not to mention I am a certified contortionist now. I was extremely cautious with separating the connectors from the sensor and my car has the TPMS sensor also mounted to the height sensor bracket

Ready for the new sensor to arrive and then reassembly.

Interesting tid bit of info, I see and have been calling this sensor a "ride height sensor" as seen on various parts distributors but FCP Euro's part description calls it a HEADLIGHT LEVELING SENSOR and I sought clarification on what I was needing regardless of the name.

BOTUS

when cars first got xenon's (EU felt too bright and dazzling - thus mandated self leveling headlamps) so they put some budget rubbish on a suspension arm to inform the car what the loading was - in a moment of madness some halfwit felt this budget fragile junk was safe to use on a critical safety system....

Ultrakla$$ic

The rear sensor is ordered, however, at present I'm working on the car with 2 floor jacks on each side with the rear wheels suspended in the air so I can work under the car with enough room. My question now is, when I put the new sensor on the car, do I place the arm of the sensor in the position that would mimick the car sitting on the ground even though the car is in the air or does it matter???.....meaning can I just put the sensor on, attach the sensor lever to the lowering link all while the car is suspended in the air then let the car down equally on both sides softly to the ground then start the car and pray it works??? Or does the cars wheels have to be on the ground, replace the sensor and attach lever then start the car? With the car on the ground it's impossible to get under it but I don't want to damage the new sensor by putting it on with the wheels in the air and then letting the car down.

BOTUS

so long as there is air in the struts then jacking up or down makes no difference

if they had no air... I think I would leave the weight of the car jacked up and let the struts fill with air before applying any weight - once the level sensor has sensible data it will find the struts own heights
as for its position - not sure I think it sits with the lever pointing backwards - but its hard to see with it on the ground - must be some YouTube rubbish to confuse yourself over ?

Ultrakla$$ic

Thanks BOTUS!


Do you think this Scanner message will clear on its own after I put the sensor back on the car, plug it back up and turn on the ignition???

BOTUS

..... get the sensor back on - leave the gateway to sleep disconnect it for 20 mins (which ever battery set up it has) - reconnect see what it says ?

if its stupid see what the three height sensors are saying - go from there...