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1994 E420
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285 Posts
Discussion Starter #1 (Edited)
2 issues:
  1. The central locking mechanism stopped working on my '94 E420. The doors will not lock when I use the key on any of the exterior locks.
  2. The rear headrests will not retract when the dash switch is depressed.
Any advice regarding the repair of these 2 items would be appreciated. Thank you.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,618 Posts
Sounds like your vacuum pump stopped working. Should check into that. Do you hear the pump running when you activate the central locking system.
Also there could be a significant leak in the vacuum system that the pump can not overcome.

94's still have the vacuum system, correct?
 

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Registered
1994 E420
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285 Posts
Discussion Starter #3
dolucasi: Thanks. Yes, it has the vacuum system. That and the headrests worked fine until I took it to an upholstery guy to install an Alcantara headliner. & no, I don't hear the vacuum pump working when I turn the key in the door lock.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,618 Posts
If you are sure it is not running, it probably is busted or the fuse it is on is blown. You'll have to chase that down.
Check for voltage, etc.
 

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1995 E220
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532 Posts
Most likely headrest vacuum line is open, headrest works with engine running and does not depend lock pump.
 

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Registered
W124, 1991ish 250D
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5 Posts
Hi 1994 E420,

It sounds like a vacuum pipe or pump failure.

There are two vacuum systems on the W124. One is engine generated, t'other uses an electric pump under the right-hand side of the rear seat.

The electric one runs the central locking and nothing else.

The engine one does some enginey stuff (injector start/stop, tick-over advance in cold weather &c on Diesels), headlamp angle adjust (the dial next to the headlamp switch) and rear headrest fold.

An easy way of checking if it's the engine vacuum pump or the central locking pump - With the engine running, does the headlamp beam adjuster work ? If not, either the pump has failed, there's a leak in the pipework or the rear headrest solenoid valve has failed.

The central locking no longer works - does the pump motor beneath the R/H rear seat whine or hum when you lock or unlock the doors ? It should run for five or ten seconds then stop. If it runs for more than that there's a leak in the pipework. Easily found by listening for and locating a hissing sound.

The rear head restraints don't go down when you press the dashboard button ? i've got the same problem on my current W124. The solenoid valve has failed (again, under the rear seat cushion, left-hand side). Mine doesn't close properly making the engine vacuum system not work.

Ok, i do enjoy mucking about with my W124, my current one is my second in about 15 years. i've had this one, "Sally" for about three years.

If you're prepared to do a bit of occasional mucking about with your car, the W124 is perfect. The last proper car Mercedes-Benz ever made. Beautiful, safe and comfortable.

All the best,

Neil xx.
 

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1994 E420
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285 Posts
Discussion Starter #7 (Edited)
PhantomLord: Thanks. I didn’t realize that the headrests worked on engine vacuum.

Old Redbeard: Thanks for the information. I was preparing to take out the rear seat when I thought I’d check the fuses again. These ageing eyes of mine missed the blown fuse in the “C” location, which I replaced. This repaired the central locking issue. I then removed the fuse in the #1 location which was ok, so I put it back in place. Under the hood, I thought I’d check the vacuum junctions – particularly the “Y” junction (part #1190940312) which I replaced a year ago w/ a Chinese part - I think it was a URO brand part - I knew they were blowing out some oil. Sure enough, that Y junction was all swollen and soft. I don’t think this vacuum junction has anything to do with the rear head rests, but I put small hose clamps at each junction to prevent any leaks until I can get a genuine one ordered. The rear headrests are retracting properly now.

I agree that the W124s are the last of the great over-engineered Mercedes and I work on mine all the time.

Thanks to everyone for the advice.
 

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Premium Member
1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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7,034 Posts
note that the electric pump for the door locks is not really a vacuum pump, rather it is a push-pull pump... it goes one way for 'lock', and the other way for 'unlock'... this module is in a foam box under the back seat.
 
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