How does the central locking system work. - Mercedes-Benz Forum
 
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#1 (permalink) Old 04-16-2006, 11:51 PM
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How does the central locking system work.

How on earth does the door locking system on these cars work? I’ve been going through the interior of the car, and while I had the door panels off I checked all the hoses, and wires to the lock actuators to insure that they were still good (all of which were). However, I have no clue how it is suppose to work. Is there an electric signal sent from the door to the pump when the key is turned, and that signal tells the pump to turn on and create the vacuum needed to lock or unlock the rest of the doors? If I knew HOW it worked, it would really help on trying to fix it.

Thanks in advance for your help.

"Some people are like a Slinky... Not really good for anything, but you can't help but smile when you see one tumble down the stairs."

1984 300SD, light blue exterior, dark blue interior, 240,000 miles.
Ira Cody Patterson,
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#2 (permalink) Old 04-17-2006, 06:10 AM
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RE: How does the central locking system work.

You got it. Each actuator has a switch, that sends a signal to a pump in the trunk. It is with the spare tire. It pumps pressure or vacuum to move the actuators.
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#3 (permalink) Old 04-17-2006, 07:33 AM
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RE: How does the central locking system work.

So theoretically (though, I’ve never been a fan of theoretics), if I have someone stand by the trunk with the lid open, put the key in the door, lock and unlock, the person standing at the trunk should be able to hear the pump kick on. And if the pump is not kicking in, I have an electrical problem I have to address before I can start worrying about the vacuum system. Is the correct?

Thanks again for the help.

"Some people are like a Slinky... Not really good for anything, but you can't help but smile when you see one tumble down the stairs."

1984 300SD, light blue exterior, dark blue interior, 240,000 miles.
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#4 (permalink) Old 04-17-2006, 08:29 AM
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RE: How does the central locking system work.

I shouldn't think you could get the locks to cycle with the trunk lid open. I think it should be latched for that to happen.

I can haer the trunk lock cycle when I actuate the system via the L/F door lock on my SEC.

Cheers, MBL
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#5 (permalink) Old 04-17-2006, 08:43 AM
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RE: How does the central locking system work.

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#6 (permalink) Old 04-17-2006, 08:48 AM
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RE: How does the central locking system work.

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#7 (permalink) Old 04-18-2006, 12:31 PM
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RE: How does the central locking system work.

Hi,
Ive only just sorted out the central locking on my 1990 500sec. The locks do cycle with the boot lid open, or mine did anyway!

There is a really easy way to test your electrical signals from the doors without pulling your door trim apart to get at the actuator. On my car there is a round 3 pin plug going into the pump in the spare wheel well. Each one of the pins is a +ve terminal for each of the doors:

1 for the passenger door,
2 for the drivers door,
3 for the trunk lid.

Get yourself a 12V light and push the +ve wire on the light into ONE of the 3 pins. Now connect the -ve wire of the light to the cars body (make sure its a good earth). Now go around the 3 locks on the car and turn the key in each lock untill you find the lock that makes the light turn on and off.

If all three terminals make the light go on and off from the three different locks then your door actuators are fine and are sending the signal....so its your pump that needs replaced

A MUCH easier way than trying to figure out all the wiring diagrams.......hope this helps!!

Alastair.
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#8 (permalink) Old 09-19-2014, 07:11 PM
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Noone of mine actuators works, even if the compressor starts correctly from all positions; Front left & Right + trunk. I disconnected the hose from the compressor, and sucked (!) the hose. All door actuators did close. OBS! Do not forget the key inside if you dont have any spare key!!!!. However, if I try to open by blowing into the hose, nothing happens? May be I am not able to blow hard enough, as the compressor dont give enough pressure/vacuum???
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#9 (permalink) Old 09-19-2014, 10:22 PM
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Welcome, how to complete your profile, search the forum archive, and the link the the W126 service manual can be found Mercedes-Benz Forum - Announcements in Forum : W126 S,SE,SEC,SEL,SD,SDL Class
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#10 (permalink) Old 09-20-2014, 08:16 AM
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Sadly I've noticed mine has once again stopped working from the driver door, but that's ok because it's usually just me in the car (THAT is why I want/need a coupe ). The passenger door rod broke a while back and just never have fixed it and I usually leave the boot locked, key pulled in horizontal position

My Stable:
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'98 Yota RAV4
'02 S-10 Truck
'72 SeaBird boat, overhaul on hold
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