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Old 01-11-2005, 06:55 AM
Join Date: Jan 2005
Posts: 33
W140 trunck lock problem

My W140 had a problem with the trunck lock. This is the story:
When I push the trunck unlock button the trunck open BUT the handle does not come out. I then close the trunck and the vacuum does not close the trunck. I have to slam it and the trunck close. I can hear sound from the trunck when open and close.

From this another problem follow. I use my keyless to lock and unlock the doors but it won't lock. However the door will close (ie the vacuum works here).

I have open the trunck cover and don't know where to start. Please help.

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Old 01-11-2005, 04:45 PM
Registered User
Join Date: Sep 2003
Location: Dallas, Tx
Posts: 701
Try resetting your pnuematic pump first. You accomplish this by removing a fuse, I have not had my 140 in over a year, so I don't remember which one it is, give that a try, if that doesn't help, then check for vacuum leaks by disconecting each line and putting vacuum on it to determine if there is a leak. The pump in a 140 is located behind the trim on the drivers side in the trunk, it is shoved back in there between the gas tank and fender. The pump has insulation on it to isolate the noise. Be gentle with it, the lines are plastic and can be broken easily. Good luck!
Brian W. Heitman

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Old 01-14-2005, 06:26 AM
Join Date: Jan 2005
Posts: 33
Fuse - unplug and plug, no difference.
Close and open trunck - the vacuum pump under the seat works. So not the pump.

Trunck handle vacuum line - apply air or vacuum, the handle open and close. So not this vacuum line.

Trunck lock vacuum line - Apply air and vacuum to vacuum line at vacuum pump end, found no flow. Apply air and vacuum to vacuum line at trunck lock end, found there is flow.

What happen please help.
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Old 01-14-2005, 06:49 PM
Registered User
Join Date: Aug 2002
Posts: 179
similar situation

When I first bought my W140, I had the same problems the doors would self seal but the trunk handle would not always extend or retract and the trunk would never close on its own. I obviously never figured it out except, 6 months after purchasing the vehicle, the pump went south. Dissassembly showed one motor brush severed in half and the other with just a hair of brush remaining.

Once the vaccum pump was repaired, the rear units started working properly (even the backup guide arials until my son tried to help and push the arial in subsequently rupturing one of the internal diaphrams.)

So, in all probability, the vaccum/pressure pump motor in yours is weak and not supplying sufficient volumes of vaccum/pressure. Unfortunately its an expensive replacement.

Best of luck though. If you know someone with a working unit (friend, partner etc), try substituting their pump and see if everything works.

1995 E320 -171k-km
1995 S420 -333k-km

Last edited by tower; 01-14-2005 at 07:56 PM.
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Old 01-14-2005, 08:57 PM
Registered User
Join Date: Jul 2003
Location: Tulsa
Posts: 304
The pnuematic system pump (PSE computer) has different "jobs" which including door locks, back-up assist (depending on your model), headrest fold-down (rear seat), ortho-seats, retractable trunk handle. This is the pump that is located under the passenger rear seat.

The PSE pump DOES not control door closure assist. Door closure assist is controlled by a separate pump located in the trunk next to radio amp on the driver’s side.

As always, check the fuses at a 1st step. (in the trunk fuse panel) I cant remember if this is fuse # 9 or # 3 .. check your diagram) By removing the fuse and reinserting the fuse, after waiting a few seconds you can reset the pump sometimes providing a temporary fix to your PSE pump problem. (kind of like reboot a computer) If the pump is working you will also hear a humming noise coming from under the rear seat location when the system is activated.

As a side note: If the system senses a leak it also shuts down, but after resetting you should hear it run. There is a 10 second shut down in locking and a 60 sec shut down in consumers. I would try the keys since they control the pump directly.

PSE pump failure is common in our model of MB. I think the dealer part cost is about $750. If you’re mechanically inclined you can find a replacement pump and install it yourself. Phil at Fastlane can give you a better price. FYI.. MB has moved to “universal PSE” pump, so you may need additional hose connectors to complete your replacement.
Russell McMahon
Tulsa, OK

2001 CLK 320
1992 400se
1993 400e
2000 320ML
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Old 01-16-2005, 11:44 PM
Join Date: Jan 2005
Posts: 33
Thank you for all your tips. YES it is the pump. I fix it myself and I am very lucky. I spend on parts for only less than US1.00 BUT time wise, it's about 12 to 15 hours.

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