it's a 2008 S550 4MATIC with air shocks. I've had it 4 years never an issue with the shocks. Almost never have anyone in the back seat, but tonight had a 250 pound friend in the back seat. Went to dinner no problem, but getting back in tehe car after dinner the rear shocks were completely bottomed out and I had the message MALFUNCTION in the dash with the suspension picture . The rear suspension took every imperfection in the road very hard. I tried using the button on the center dash to raise the air shocks but it didn't do anything. I don''t thing the shocks failed but rather some sensor / switch that controls the rear shocks went out. Something else odd happened at the same time. The DVD player came on in the dash and the driver side mirror changed positions at the same time the shock issue started which I find weird.. What do you think this could be?

 

Hey there,

It is possible that since you are getting the front air struts to engage and air up and it is only the back that is not engaging and airing up, that you may have an issue with the valve control block. I would say it is suspect that both went out at the same time, and I also seem it is coincidence that it went out with a passenger, but it could have been compensating while driving and what not for the added weight using the leveling sensor and then something failed within the valve block. Just throwing that out there.

2008 S550 Airmatic Valve Block | Mercedes-Benz Forum

🧩 How the Airmatic Valve Block Works

The valve block (or valve unit / distribution block) is a central air manifold that controls airflow between:

• The Airmatic compressor
  
• The air reservoir (tank)
  
• Each individual air strut (front left, front right, rear left, rear right)
  

It’s an electrically controlled solenoid block that opens and closes valves to:

1. Inflate or deflate each strut independently.
   
2. Maintain ride height using signals from the level sensors.
   
3. Direct air to the reservoir tank for pressure storage.
   

On the W221, there are two valve blocks in some configurations:

• One main block (under the hood, near the compressor).
  
• A secondary rear valve block (mounted near the rear axle subframe, especially on 4MATIC models).
  

⚠️ What Happens When It Fails

If the valve block leaks, clogs, or the solenoids fail, you’ll get one or more of these symptoms:

🔻 1. One or more corners won’t lift (often rear only)

• The compressor runs but air never reaches the rear struts.
  
• You might hear hissing or feel no air at the rear airline fittings.
  

🔻 2. Car drops overnight or sags unevenly

• Leaking internal seals allow air to bleed back through the block or vent valve.
  

🔻 3. Compressor overworks or times out

• The system tries to compensate for pressure loss, triggering “Airmatic malfunction” or “Car too low” warnings.
  

🔻 4. No airflow even though compressor works fine

• Solenoids fail electrically or get stuck due to moisture/contamination.
  

🧰 Diagnosis Tips

1. Listen for the compressor:
   If it runs for a while and shuts off with no rear lift, suspect the valve block or a rear airline issue.
   
2. Check power to the rear solenoids:
   You can backprobe the connector and verify the ECU is commanding the valves.
   
3. Spray soapy water at line fittings (when aired up):
   Look for bubbles around the valve block or lines — it’s the easiest leak test.
   
4. Scan codes with MB II / Star Diagnostic:
   Codes like C1567-001 (rear valve block leakage) or C156E-001 (valve relay faulty) will confirm it.
   

🔧 Replacement & Cost

• OEM replacement (W221 Airmatic valve unit):
  Part number: A2213200358 (or superseded A2213200458, depending on your VIN).
  
• Average price: $60–$130 on eBay or PartsGeek.
  
• Location: On 4MATICs, the main block sits behind the front bumper near the compressor; the rear block (if equipped) is mounted above the rear axle.
  

Replacement is straightforward:

• Depressurize the system (via scanner or slow manual venting).
  
• Disconnect lines carefully (mark them).
  
• Swap the unit and clear codes.
  

✅ Bottom Line

✔️ Yes — the valve block does send air to each strut individually.
✔️ A failure in that block can absolutely cause just the rear to not air up, even if the compressor and lines are good.
✔️ It’s one of the most common causes for “rear sag / no lift” after leaks and level sensor faults.

 

your LEVEL sensor link rod has snapped off - normal design feature

in the photo below the bracket top right will still be on the anti-roll bar - but the rod will be dangling - the ball joint seizes till the metal fatigues bending back and forth after it seized up last year

nasty job - cheap part $45 - plus risk of death at the side of the road - NEVER drive with it bottomed out

 

Thanks for your reply BOTUS. I did drive 20 miles homes last night, mostly highway and it was rough. What is your comment about death at the side of the road though? Are you talking about some danger when replacing the broken level sensor link rod?

 

Since they both collapsed at the same time, either a valve block or rear height sensor. Sensor is easy to diagnosed by just looking under the car and see if it is dangling. Botus is on point, nasty job!

 

I drove 1/2 a mile at 20 mph it was utterly horrific - it allegedly doesn't do the airbags any good - but I'd be more concerned the body mounts are sill there and not fractured on the bodyshell

as you found there is nothing holding up the weight of the car up but air - if the air comes out whilst you are underneath 1.5 tonnes will squash you and nothing you will do will stop it

flat location - park and park brake enabled - jack the car up on the left front jacking point just enough that a trolley jack will fit under the left rear jacking point, take the weight to normal ride height and loosen the rear wheel bolts.... jack it up remove rear wheel

with glasses and a very bright torch trace the rear anti-roll bar (ARB) from the left disc area along the bar... thus looking in about 2 1/2 foot from the side of the car, just in front of where the front edge of the rear tyre would have been...

you should just make out that rusty bracket on the anti-roll bar... now look around this area and likely will see the link rod to the rear level sensor with a bit of the bracket left on the seized ball joint... if lucky there should jet be enough left you can get a worm drive clip on the ARB and reattach the two - I did it and drove gingerly 30 miles to a garage that hated me for going there - they broke two new link rod assemblies trying to replace the bit in the photo in 3hrs !!!!

its a super unpleasant job and its not possible with the ARB on the car to get the ridiculous click together clamp to go together without damaging it - don't bother to try - find the flat on the ARB indicating the correct angle to attach the lower ball joint bracket and using a stainless worm drive clip (that you ground a smidge off the width to sits within the lower ARB bracket) and do it up better than Merc manage at the factory - not tried - but maybe if an animal / side of the road fix the upper ball joint could be popped off it ball lubricate heavily and pop the new black plastic joint on the old ball which is obviously on the lever of the level sensor up in the gods

for those with air tragic - I think this breakdown and the amp dying will happen to every single owner

 

Having my car towed to my indy mechanic tomorrow. I hope i didn't damage the airbags on the shocks after driving 20+ miles last night. Some of those bumps were friggin harsh!!

 

the worm drive refit of the new linkage is a 45 min job - half the lemmings charge upwards of 6 hours to remove the whole rear axle

 

I just installed the K-Mac bushings and for the left side one I had to take the emergency brake module loose to be able to get the bushing bolt in from the rear direction. I noticed that it gives lots of more room to get hands to the level sensor area.

 

UPDATE: I took the car to my indy mechanic and he confirmed the level sensor link rod snapped. He replaced it and is having the following issue. He can use some computer he has to raise the car and the get it back to ride height but they eventually deflate again. Does it sound right that I would have to bring it to the dealer to have something recalibrated using their proprietary software? The mechanic thinks that the rear air shocks are still OK.

 

Probable damage from being deflated....

 

Likely problem is the rod is oriented incorrectly. It should look like this: / Rod end connected to sway bar is lower, rod end connected to sensor is higher.

 

has happened before - I think you can flip the lever on the sensor so its 180 degrees out arm pointing forwards not backwards

but 20 miles and the airbags won't have liked it

 

If you have a DAS/Xentry you can always do a leak test, so that you know if it's the shocks or not.

 

UPDATE - it was the level sensor rod which had rusted through and snapped. My mechanic replaced it and couldn't get the car to rise with the tools he had. He called in a Mercedes mechanic who had the proper diagnostic MBZ computer to calibrate the air shocks and was able to get the car's shocks to where they should be. I've been driving the past few days and all is well. It's been close to freezing and the car does not drop overnight.

Was worried the rear shocks might have been toast since I drove 20+ miles on them when the rear of the car was dragging ***, completely bottomed out. I felt every tiny bump on the way home, and medium bumps were HARSH. Dodged a bullet for sure.

 

I had a 2013 S550 and I lost the Front Left strut 330 miles away from home. I drove it back home and it did not cause any damage to the mounting point of the strut. What is the worst case in it other than mounting point damage - the strut goes all bad. Well, it was that already so what...

 

...dude there are people who drive those things exclusively with blown airmatic

that many miles won't be anything. To give you an idea, I repair cars that hit a curb completely perpendicular at 30mph, the STRUT is bent with nothing else being damaged. The stuff is built real strong. You caught it and do the right thing immediately so I wouldn't worry.

 

Happy to have the S550 back, so I gave it a good detailing yesterday. Looking sweet!