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WADAN 02-03-2001 07:35 PM

Recently, I purchased a 1992 400SE. Upon reading the owners manual, I became aware that there is a pneumatic door assist in the normal closing of the doors and trunk lid. This system is not functioning at the present time. ( None of the doors or the trunk lid pneumatically close, they must be "slammed" closed. ) Is there something simple that can be checked by me before taking it in for service?

Thanks in advance....


BmwTek 02-03-2001 09:48 PM

most likely your vacuum assist pump in the trunk is bad..
but you can check fuses 3 and 9 in the trunk.. if they are good.. jsut remove them wait 60 seconds and put them back to reset the system.. it may end up fixing the problem, but if prior abnormalities persist your vacuum assist pump PN 140-800-08-48 will have to be replaced.. it costs about $570 and is like a .5 hour job..

good luck..

my opinion.. dont even worry about it... jsut let it be and just enjoy the vehicle.. oh and you should know about the more typical faults the early w140's had such as front end shimmy, the AC evap. adn the window reg. that tend to snap..

good luck and have fun with your W140.. i have 165k on my M104 powered 300se.. and its been great even without the power assist not working.. hehe..

MBenzNL 02-04-2001 08:25 AM


I know that the US clients were and are spoiled by mercedes, but the pneumatic door assist was an option in europe... Not every W140 S-class has that option here and I do not whether it was an option in the US or not, but with the dutch W140 we have to "slam" close most of these doors...
I presume that the american models do have this gadget as a standard item...


WADAN 02-04-2001 03:34 PM


Interesting point that you bring up, this is a Canadian W140. This is the first Mercedes that I've had the pleasure of owning, so I had noticed in the owners manual that there was this option. Ofcourse I don't know whether it was a standard option or not. BmwTek did give me some info about the location of the vacuum pump ( in the trunk ), so my first move will be to see if there is a pump at all and go from there. Thanks to all...


David C Klasse 02-05-2001 01:12 AM

To my knowledge, the early year 140s, 300 and 400 (320, 420) did not have pneumatic doors as standard feature. I do not know at what year this became standard.

BmwTek 02-05-2001 08:41 AM

I dunno but i am pretty sure it was standard on all US models.. not def sure... but pretty sure..

so any luck with reseting the system?? did it work??

Oliverp 02-05-2001 09:55 AM

I have this problem as well. I have survived on just taking out the fuse and putting back in. It will work for about a week, and then fail again.

The doors I'm not that bothered about, it's just the trunk. If the closing aid fails, the trunk tends to bounce when you try and close it. You have to mess around with switches in the trunk to turn off the closing aid. Sometimes, when the aid fails, the trunk doesn't close, and the pop out handle stays open.

BmwTek 02-05-2001 10:12 AM

jsut disable the trunk closing feature via the switch on the trunk lid,,, if it still tends to bounce up its probably the hinge on the locking mechanism... (located on the car itself not the lid.. basically all you have todo is remove the cover and you will see 2 bolts.. just position them correctly and tighten them up.. you should be fine..

MBenzNL 02-05-2001 05:06 PM


There will be a pump when you are going to "search" for it. It is the vacuum pump that controls the:
* central doorlock,
* AC ventilation vacuum pods,
* orthopaedical adjustable seats,
* pneumatic door assist.

...just to let you know...

tivoliman 05-01-2005 03:26 PM

Disabling it sounds good - How
The trunk closes and locks, but the vacuum assist isn't working.

How do I get the trunk to close completely?
The "locked position" now is at the top of the vacuum pull down, so water may leak in the sides of the trunk lid.
1 - How do I get the trunk latch to "lower"?
2 - How do I get the trunk vacuum assist to stop assisting?

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