W124 central locking

[W124newbie]

Hi,

If a w124 only opens the particular front door or boot with the key, and none of the others, but you can hear the pump going for 20-25 seconds after turning the key... Does that sound like the pump needs replacing or a possible air leak somewhere?

 

[GP801]

Its probably a leak somewhere. The pump lives under the rear seat squab. Usually wrapped in foam.

 

[W124newbie]

Great, I was hoping it would just be the pump so it could be replaced and problem solved!

I'm guessing its quite tricky to find the source of the leak and fix?

 

[trapperjohn]

Probably just the pump. After that - nightmare!!

 

[219]

There's a video on an American website ( I'm away from home and typing this on my phone , so I'll probably have to wait until I get home to look for it ) where the guy shows how to diagnose and fix central locking vacuum faults on a W123 - the system is basically similar except the 123 uses vacuum from the engine rather than a pump .

He has a logical way of following the vacuum around the system and determining where the leak may be .

I will try to find it and post a link .

EDIT - luckily I had the site bookmarked on my phone , link to specific video below , there are lots more on the general site

https://mercedessource.com/node/8553

 

[kth286]

the petrol flap ofter causes problems on 124.

So, press key for central locking, OR insert key into lock and turn.

Whilst, everything is now trying to work, go to flap and open it.

If you can open it, the module is likely faulty, and will cost approx £18
to buy new from dealer (last time).

It's just a plastic assembly and easy to access behind the trim in boot area.

 

[Dec]

You need to first establish if you have a leak, to do that you need to remove each Yellow tube and blow/suck hard through it.

By blowing through a tube you will unlock a locked door… door pin will pop up.

By sucking through a tube you will lock an unlocked door… door pin will drop down.
Same thing for the boot and petrol flap.

You won’t be able to blow (or suck) any air continually into a Yellow tube that doesn’t have a leak….if you can blow continually into a tube then there must be leak.

If there are no leaks in the system then it might be possible to make an adjustment inside the vacuum pump to reduce the 20-25 second running time down to 2 or 3 seconds

How long does the vacuum pump run for when you lock the car?
How long does the vacuum pump run for when you unlock the car?

Dec

See also… PeachPartsWiki: Keyless Entry Install

 

[alfajuj]

I'd like to add a few words to this old thread as at the moment I am working on the central locking in my W124 (It's a 1993 280E) There are two main problems:

Problem one:

The key in the driver's door usually only opens or locks the driver door only-the other doors won't lock. After stripping the door panel, I wiggled the wires to the actuator and sometimes I can get it to work as it should. ie. It will lock or unlock all the doors and if the windows are open, it will close all the windows if the key is held in the lock position.
So the most likely cause is a broken wire in the signal wire or bad contacts in the actuator.

Using the key in the trunk works as it should. It locks centrally and also closes the windows.

Using the key in the passenger door, it locks centrally but does not close the windows. (I suspect that the passenger door does not have the window closing function???)

Problem two:

When the doors lock, the pump runs for a few seconds as it should.
But when the the doors unlock, the pump runs for a long time, maybe 20 seconds.
This means there is a pressure leak in one of the actuators.

If you let the pump run on like that every single time it locks, the little motor in the vacuum pump will definitely burn out.

So I went to the vacuum pump and pulled the yellow vacuum lines one by one. to check for a leak. (it's a lot easier than pulling all the door panels) Using ones mouth to test did not work for me. I used a pressure tester. But a bike pump with a gauge would work too.

Success. I found the bad actuator. It was in the right rear door.
I replaced the actuator and now the pump runs for just a few seconds on lock or unlock.


Great. It worked fine yesterday,
But today, the central locking doesn't seem to have the strength to lock the doors now!!!

 

[Dec]

Are you using the boot lock or the door lock to lock/unlock?

How many seconds does the vacuum pump run for when you lock the car?
How many seconds does the vacuum pump run for when you unlock the car?

Dec

 

[alfajuj]

Yes, I can use the boot lock to centrally lock or unlock the car, and can also close/open the windows.

The passenger door can also centrally lock or unlock the car but cannot close/open the windows.

The driver's door usually only locks or unlocks itself.
When it is in a good mood, it will occasionally centrally lock or unlock the car and when it does, it can also close/open the windows.

This leads me to believe it is likely an electrical fault in the signal wire in the driver's door. I think it is probably a broken wire in the area where the wiring routes in the door jamb. I am trying to figure out how to get into the kick panel area. It seems that the interior panel in that area is a very large and continuous piece.

Before I replaced the rear door actuator:
The vacuum pump would run for about 3 seconds or less when I centrally lock the car.
The vacuum pump would run for about 20 to 30 seconds when I centrally unlock the car.
But after replacing the actuator, that works fine.

Yesterday, when I found that the central locking didn't seem to work at all, I later realized that the battery was almost completely flat.

 

[Dec]

I would start looking for a fault at the vacuum pump and its connections to see if the are sound and possibly opening up the unit up in the hope of identifying a bad solder joint or other fault on the PCB. W202 unit pictured below should be similar to yours.

The vacuum pump is connected to the Comfort control unit, picture below, this unit controls the up and down of the windows, that must be working ok as there is no problem when you use the boot lock.

If its not the vacuum pump that’s at fault then, as you suggest, it must be a bad wire at the door hinge or the door lock switch itself is a bit hit and miss.

Does the key make a full quarter turn, left & right when, you lock/unlock?


Dec

 

[alfajuj]

Thanks for the photos!

Yes, the key makes a full quarter turn both ways.

I will look at the wiring through the door hinge next. How do you access the wiring once it passes the from the door hinge area and into the car? Seems that I may need to remove a lot of panels to get in there.

After that I'll replace the driver's door actuator if the wiring is sound. It's less likely, but the contacts could be dodgy.

As the absolute last step, I'll go into the vacuum pump itself and look at the PCB.

By the way, is it normal for the passenger door to not have the close windows function??? It seems strange that the boot works but the passenger door doesn't.

 

[Dec]

Don’t know the W124 so can’t advise about wiring at door hinge.

Others may advise but I would have thought that the passenger door lock function is solely for emergency entry into the car if access were not possible through the driver’s door… if you were blocked in at a car park for example.

The boot works as the boot is sometimes the first thing that is opened by the driver…to put in a briefcase for example.


Dec

 

[tjamesbo]

Holy Thread resurrection
37 seconds to Lock (suck cycle)
5 seconds to unlock
Fuel Filler cap ( estate ) not locking
Opened up Compartment Cover and can hear it sucking Air !
Fuel Filler cap not locked for years never worried about it
But Did notice that if you locked the car you had to wait almost a minute ( 37 seconds in hindsight ) to be able to unlock it, just thought it was a quirk of the system .......... should have known better, mercedes engineers wouldn't have allowed that, obviously what was happening was the motor was still sucking till it timed out
So Many Years Later all becomes clear
Just need to get myself a new Filler cap lock diaphragm assembly
(perhaps temporarily bung the end up )
This Thread was SPOT ON