Airmatic question, sometimes sits low in the rear when I turn off the engine and sometimes it looks normal for days?

Tiny
SEBASTIAN1980
  • MEMBER
  • 2002 MERCEDES BENZ S500
  • 2WD
  • AUTOMATIC
  • 117,000 MILES
I notice my vehicle listed above sometimes sits low in the rear when I turn off the engine, and sometimes it looks normal for days. Also, I noticed that when the height of the car looked normal and when I opened the car door and the trunk. It started to sit low again in the rear. No signs of leaks when I checked all the lines and the airbag strut. I do hear the pump coming on, so I assumed the air pump might be good. I did check all the level sensors and the arm that's holding the sensor, and they looked okay, nothing bent and loose. Please, I need your help and maybe your opinion on where to look for and how to diagnose my next option. I don't have a lot of money to take it to the shop as I have just moved, and I am looking for a job. Thank you in advance for your time.
Sunday, December 29th, 2024 AT 12:44 PM

7 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,240 POSTS
From the description it sounds like one of the dump valves isn't seating properly every time. The way the system operates is by determining a level car, you get in or put weight in the trunk, it determines the rear end is low and adds air. You drive to wherever and remove the weight, the car then determines it is too high and opens a solenoid to release air until it's level. In your case, that valve sometimes doesn't seat fully, and it leaks. The biggest reason this happens is because of moisture in the air. Whenever you compress the air its get hot. The air also contains moisture. That warm moist air gets pushed through the system. It contacts all the areas that have metals, and they start to corrode. Then you get leaks if the corrosion is in the valving or fittings. Your car does have an air drier on it, but I suspect it's the OEM unit that hasn't been operating and it's letting wet air into the system. As such what you really need to do would be to pull a vacuum on the system to pull moisture out. Then change out the air drier and the solenoid that controls the air. These are all mounted near the compressor at the front of the car. You can get a replacement Arnott solenoid unit for around $200 and a replacement compressor drier for around $300 through Rock Auto. To install it you need to disconnect the battery, then drain the air out of the system. Now what I usually do if I'm working on an air ride car is to go under it before I do anything and set blocks under the suspension and frame at the current ride height. Then I jack it up, do the work on it and once done I set it back onto those blocks. Then reconnect the battery. That way it shouldn't need to be recalibrated for ride height when you're done.
There is also a conversion kit, but as you state yours does hold that sort of rules out the lines and air springs and points to the valves. If I was in your place, I'd probably just replace the valve for now. It will likely last for as long as the rest of the car at this point.
Oh, and the part about opening the door or trunk causing it to lower, that is normally how they work, it's supposed to make it easier to load the trunk and ease your entry into the car. Personally, I'm not a fan of that as I dislike crawling into a car.
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Sunday, December 29th, 2024 AT 2:46 PM
Tiny
SEBASTIAN1980
  • MEMBER
  • 15 POSTS
Thank you so much for sharing your knowledge, and definitely will follow your advice.
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Sunday, December 29th, 2024 AT 10:36 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
STEVE W. Is one of our best! Please let us know how it goes :)
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Thursday, January 2nd, 2025 AT 9:57 AM
Tiny
SEBASTIAN1980
  • MEMBER
  • 15 POSTS
Hello Ken and Steve,

So I replaced the valve block finally and now I'm having a problem with the pump. Before I replaced the valve block. The pump was working just fine, but after I put in a new valve block. The pump won't come on. I checked all the lines and fuse and everything looks correct. The fuse looks good and the wirings are in the proper location. One thing that strikes me, though, is that. I heard and felt a click consecutive times where the valve block connector is and the pump harness is connected to the valve block. So I assumed there is power going through the system. Please help and thank you once again for your input.

God Bless
Sebastian
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Sunday, January 19th, 2025 AT 3:31 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
It sounds like you may have something stuck inside the air pump, let check the power and ground inputs here is the wiring diagrams so you can see which wires to test and a guide to help with the test as well.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Also, check the ground at the right front wheel well. I have marked the power and ground on the wiring diagrams for you. Check out the images (below). Please let us know what happens.
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Tuesday, January 21st, 2025 AT 10:12 AM
Tiny
SEBASTIAN1980
  • MEMBER
  • 15 POSTS
Hi Ken,
Thanks for the input! I did figure out what exactly happened. I forgot to screw the ground back to the wall of the car. Thank you for helping me out and have yourself a wonderful day.
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Monday, January 27th, 2025 AT 10:16 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
Thanks for letting us know, we are here to help, please use 2CarPros anytime.
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Tuesday, January 28th, 2025 AT 9:42 AM

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