Dynamic seat check valve?
Thread Starter
Junior Member
Joined: Nov 2020
Posts: 22
Likes: 1
W220 S55 supercharged
Dynamic seat check valve?
The driver side dynamic seat bolsters on our 2006 S55 want to work - the outboard bolster will inflate but won’t hold pressure. As soon ans the outer Bolger inflates, pressure escapes with an audible hiss that sounds like it is coming from under one of the seats but can’t tell if it’s on the driver or passenger side.
I believe the leak is isolated to the driver side. The passenger side bolsters work fine and the pump doesn’t seem to time out.
To troubleshoot, should I begin by taking the rear cover off the driver seat and having a helper listen for the leak/hiss near the valve block? I believe there may be a check valve located to the side of the valve block but I haven’t had any luck finding a part number.
Has anyone had a similar issue? What was the fix?
I believe the leak is isolated to the driver side. The passenger side bolsters work fine and the pump doesn’t seem to time out.
To troubleshoot, should I begin by taking the rear cover off the driver seat and having a helper listen for the leak/hiss near the valve block? I believe there may be a check valve located to the side of the valve block but I haven’t had any luck finding a part number.
Has anyone had a similar issue? What was the fix?
MBWorld Fanatic!
Joined: Dec 2012
Posts: 2,474
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From: Ball Ground, GA (N of Atlanta)
2003 S500 2007 GL450
Possible diagnostics:
- Get 4' of 3/8" tubing (or similar). Stick one end in your best ear, use the other end as a locating device to find the leak. Check under both seats before starting disassembly.
- Get a smoke generator, hook it to the line to the actuator (plastic bag). Watch for leaking smoke. The smoke generator is not terribly expensive, and is useful for checking for vacuum leaks in all of the intake gaskets, seals and tubes, as well as all of the PSE tubing.
If the leak does not appear to be under one of the seats, and the 2006 is like the 2003 cars:
- Run the seat forward just enough to access the back cover.
- Lift the rear as high as it will go, and lower the front..
- Run the seat-back as far forward as it will go.
- Look under the bottom of the plastic cover, and remove the two screws.
- Pull the seat-back cover, exposing the tubing, actuators, etc.
- Get 4' of 3/8" tubing (or similar). Stick one end in your best ear, use the other end as a locating device to find the leak. Check under both seats before starting disassembly.
- Get a smoke generator, hook it to the line to the actuator (plastic bag). Watch for leaking smoke. The smoke generator is not terribly expensive, and is useful for checking for vacuum leaks in all of the intake gaskets, seals and tubes, as well as all of the PSE tubing.
If the leak does not appear to be under one of the seats, and the 2006 is like the 2003 cars:
- Run the seat forward just enough to access the back cover.
- Lift the rear as high as it will go, and lower the front..
- Run the seat-back as far forward as it will go.
- Look under the bottom of the plastic cover, and remove the two screws.
- Pull the seat-back cover, exposing the tubing, actuators, etc.
Thread Starter
Junior Member
Joined: Nov 2020
Posts: 22
Likes: 1
W220 S55 supercharged
Thanks for the suggestions, Wally. I was focused on the distribution block in the seat back but learned the supply line under the floor to the seat often breaks because of the seat moving back and forth all the time. I do use the easy-exit feature so it’s moving frequently. That will be the first thing I check consistent with your notes. I appreciate your post!
