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Old 11-09-2004, 06:09 PM
Eiknujrac's Avatar
Car Junkie
Join Date: Oct 2003
Posts: 99
Vacuum lock problem.

Ok so I installed a keyless entry system with the proper relays in my 1991 Mercedes 300E. Everything was working fine for a couple of hours, and I was extremely happy. I think I got a little to trigger happy with the remote when the problem happened. The locks would not open with the remote OR the drivers door pin. Neither locked/unlocked the car. However, the passenger's door pin still unlocked/locked the doors. So I yank out the back seat to get to the vacuum pump. I notice that the drivers door is only sending 6 volts to the connector when unlocked (used to be, and should be 12v), and still sending ground when unlocked.

I disconnected the relays, and hooked up all the wires like they came from the factory, yet i still have the problem. The Driver's door will only send 6v. At one point, the drivers door started sending 12v while unlocked, but 4 volts!?!?!?! when locked. I am so confused.

Any help would be appreciated.


EDIT: Allready checked fuses

I love my cars to death but my wallet sure doesn't.

Last edited by Eiknujrac; 11-09-2004 at 06:18 PM.
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Old 11-09-2004, 06:27 PM
Eiknujrac's Avatar
Car Junkie
Join Date: Oct 2003
Posts: 99
Update: If I disconnect everything then reconnect it, and start with all the locks in the unlocked position, the drivers door will LOCK all the doors. I can understand this because It will still sent ground to the pump. But it will not send 12v, only 6v, and that is the reason it wont unlock. But I am stupified on why it wont send 12v.
I love my cars to death but my wallet sure doesn't.
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Old 11-10-2004, 07:06 PM
Registered User
Join Date: Sep 2002
Posts: 134
I have similar problem happened once or twice. The driver or the passanger door stops doing its job, and the other door works fine. I used to disconnect the fuse and connect it back while doors are unlooked. This resolves the problem. My interperetation is that, the central lock pump has a transistor (brain) telling it to ignore a problematic door and keep the other.However, I cannot say how this is translated into lower voltage recived? I assume that there is some rusted or not well connected things in the door locking mechanism itself. and the pump when not receiving confirmation assumes problem. disconnecting the fuse resets the pump. If you connect everything and reset using the fuse, it will work again. that is only my theory.

very problematic system!!

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