Purchased a 2004 E320 wagon with excellent maintenance records one year ago with 94K and now at 120K miles on it, the suspension lost pressure. I noticed it slightly low and then this AM it showed the error message (car too low) and is very low.

Previously I noticed a growly pump sound and was told it may be the power steering, but this happened with the engine off and at intervals while driving. Often when turning on the key there would be a pump sound momentarily and I wondered, Door lock air pump? But now I see it was the suspension pump. Its had the reservoir replaced..Im not sure how often the pump would be expected to actuate normally. Possibly a leaking component somewhere?

Fuse f37 is indicated for this on the chart. Checked all on the row and its good. I also had the window washer quit recently and the fuel gage acts up at times showing full then empty..then it works again. Bad ground possibly..?

Not a difficult replacement on the pump. So if its truly getting power and if it failed replacing this pump should correct the issue..

Could it be the control unit failing to send signal to the air pump? and how often should it be needed to come on in order to keep the system pressurized??

Just getting ready to tear into the repair and ordering parts..

Thanks for the knowlegable comments, in advance..

One or both of your airbags have failed which cause the pump to run out over time and fail as well. Find which airbag is bad. A scan tool that can inflate and deflate the airbags manually would be handy for this job. As well as read codes from the air suspension computer. When you inflate the airbags how quickly does the suspension collapse again? Does it collapse overnight?

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no it doesnt (didnt) collapse overnight and would sit easily for a week..no leak down. I see these air pumps (one model a rebuild supplier says, wears out quickly according to them and the system was very serviceable for a year..) I see various leak points other than the shocks themselves which are possible, the manifold and hoses..

You ask, tjts1, 'when I inflate the airbags...' I cannot inflate the airbags at all. The pump does not come on at all, and thats my primary issue at this point.

I may get a scan tool which could interact with the suspension, Id like to have it for working on the brake system as well. Recommendations would be appreciated for something short of a professional level scan system..around $500 or less would be very worthwhile.

Thanks so much..

Foxwell NT520. Also useful for working on SBC brakes and many other things. Should be around $150 with MB software pre loaded.

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I will try it, and start with a new pump and relay and then search for any leaks. The height did seem low but never had a warning light or truly low ride height. But I would like a higher ride in the rear. Loaded this wagon heavily a few times and the leveling seemed to work. Now my old 95 E320 load leveling was wonderful..hydraulic system and it works beautifully at 200K plus miles..And I loved the old straight six. Way better MPG and similar performance.

Thanks tjts1

Arnott makes a spring kit for this application that you can install and get rid of the air bag/compressor all together.

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I talked to a couple of people that tried that coil spring conversion and both were very unhappy with it. One actually went back to airbags. The arnott conversion is badly compromised because they reused the airbag lower control arms instead of coil spring control arms. As a result they end up using much shorter coil springs than Mercedes.

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Did anyone say specifically what they were unhappy about?

It rides like ****.

W211 factory rear coil spring 8.5 coils.


Arnott coil spring conversion 6 coils. If you look carefully you'll notice the top and bottom coil are folded in and touching the previous coil so that last coil isn't doing any work under load. Its just there to seat the spring since theres no spring seat in the Arnott design.. That leaves 4 coil doing the suspension work.


This is the factory lower rear control arm designed to work with coil springs on the W211. The spring is seated inside the control arm so the entire length of the spring can work.


Airbag suspension cars used this control arm where a single bolt holds the air bag between the 2 forks.


Both Arnott and Strutmaster half ass the conversion by reusing the airbag control arm with a shorter coil spring and an aluminum block adapter in between. It sort of works but ruins the ride quality. If you're going to do a coil spring conversion, get the control arms designed for coil springs and proper springs to go with it.

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Yes, I saw the coils offered and the reviews agree they arent great. I also see tons of promotion for code reader analyzers for only 150 and reviews say these only read the usual engine codes and that the promotions and claims they will do system analysis of components is false. So for that reason I held off buying an analyser. ($150 seems too cheap) I also found I could reset the maintenance interval warnings from the menu itself, no analyser needed. But hopefully the analyser will help me sort out the issue with the fuel gauge and the window washer pump as well as the air pump stoppage issue. And if i need to replace an air shock or other components, so be it..Thanks for the helpful info!

I've been using the foxwell nt520 only 04 E320 wagon for 6 months now. It's cheap but it can talk to every module in the car including SBC and air suspension. On top of that it can code for lower octane fuel (I run mine on 87) adjust the cooling fan ON temp down to make the AC more efficient inflate/deflate the air suspension and adjust ride height, run test routines, read error codes from the air suspension, code paddle shifters etc. Short of buying MB star SDS this is the best scan tool you can get for this car. Down side is that it's slow, not always intuitive to use and Chinese.

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Very cool info on the Foxwell scanner. My mpg is not great and I know there are some issues. Id also LOVE to adjust the ride height if possible. My model wagon does not have adjustable height as a feature, as some do..

Yes, I saw a video that also recommends this scanner highly and as you say, faults it only on speed. Id pay a bit more, happily, but this item looks exactly like what I need.

Thanks again tjts1, I see lots of great info from you here. You clearly know these cars!

One last thing
If you get a foxwell make sure it's pre loaded with the MB software. Some sellers have it blank and you have to DL and install it yourself. I've heard some people had trouble with the process and the manufacturer wasnt much help. The scan tool can hold software for up to 6 different brands. I found mine on eBay.

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Yes, I got one ordered and coming on Monday. I hate the Amazon dominance but theyre the only outfit that could deliver in two days. Other sellers were up to five days..And a great discussion of air pump replacement with the relay is on Benzworld with all the details. (no links allowed here I understand) This discussion shares the fuse and relay locations..And you tube has the replacement details on a nice video.

The info there says its often a cracked intake line allowing dirt into the compressor which messes up the seals and then it burns out. My air shocks went down very slowly so hopefully theyre still serviceable. Hopefully the airmatic system isnt fouled with junk from a compressor failure.

I got the red warning light and then the level continued going down for about two days, till they hit the pads. Full bottom. Took about a week total compression- I suspect..hard to be sure. Id like the rear to have the same tire clearance as the front but its always been a bit less with the fender arch just below the tire tread.

I looked at other models of the foxwell scanner which have other features but this 520 looks like the one for the job. And the air pump/compressors are available under $300. Not too difficult a repair..

Yes, the seller required a Merz specification prior to order completion so were good! I will probably be adding Toyota and Subaru to the unit software soon..

So you have the same Merz E320 wagon then, with airmatic and 2004. I was given an old 94 E320 and loved the car, found it easy to repair and then bought a 95 wagon for $600 bucks which was a great trip car. Totally rebuilt the cylinder head and had it nicely restored with AC and all systems good! Then smashed up in the snow..Still driveable but lost all the AC systems to front end damage.

Anyway Im looking forward to totally tuning up this 2004 and adjusting the ride height and the engine settings for mid grade fuel and checking the issues with the various bugs that come up..I owe you a short case of your favorite brew!

Thanks again! For your contributions here. These chats are more heavily focused on older cars but the depth and accuracy of information is amazing!

Okay I have an idea..Reading all the troubleshooting and issues with airmatic suspension its all focused on shock leaks and replacement, yet very likely the issue is just the air compressor pump or other system components. And what I wonder is why nobody suggests that one just "jump" the air compressor relay across the activation pins as with a fuel pump failure or the immobilizer relay or other basic relay controlled components. It seems like this option would be a quick shortcut at no risk of burning anything up. (my relay WAS badly worn and seemed not to conduct when checked with a meter so I cleaned the points, got it working fine.. still no air pump activation)

Seems like a worthy experiment..(I did notice an overheated wiring smell about a week ago plus, then it cleared up and that was that)