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  #1  
Old 08-13-2002, 06:24 PM
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300E Unlocks Itself!

My 1991 300E has unlocked itself seven times in the last two days. I lock it at the driver's door with the key...when I come back, it's unlocked - every door!

What's going on? Is my car haunted?
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  #2  
Old 08-13-2002, 08:02 PM
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This is the built-in automatic service reminder that was started in 1991.

______________________________________________

OK ... that was a joke ....

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Is it a stock car or does it have an added keyless remote system?

I have a friend who had experienced his system opening and closing on its own. It was an aftermarket system.
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  #3  
Old 08-13-2002, 08:09 PM
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The MB central locking works by vacuum. There is a vacuum pump, probably under your rear seat bench inside foam protection. This sucks the doors open and closed through pipes running to each door and the trunk.

Firstly check there is no aftermarket alarm system installed. Mine is connected into the central locking, and I think it's when one of the voltages goes 'high', the car unlocks.

I guess you could try locking the car, then disconnecting the battery. Then if the doors still unlock, it probably isn't voltage/electrics related, and so it's most likely a vacuum problem in the system. I expect there should be a failsafe which should stop the car unlocling all on its own if there's a problem with the vacuum, so I suspect there may be a bad connection causing 'high' voltage to go to the relevant wire.


Perhaps someone who's worked on their c locking can remember the wire colours and purposes? I worked with mine (wiring alarm) 8 months ago

later

Russ
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190E's:
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2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg
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  #4  
Old 08-13-2002, 08:37 PM
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Quote:
Originally posted by haasman
Is it a stock car or does it have an added keyless remote system?

I have a friend who had experienced his system opening and closing on its own. It was an aftermarket system.
This car is entirely stock. The locks have worked perfectly all these years until now.
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  #5  
Old 08-14-2002, 12:07 AM
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brewtoo,

Is this the only unusual operating behavior you have noted? When they unlock on their own, can you lock them with the key by turning it to the lock position, or do you have to cycle to the open position and then back to the lock position?

The older W123 series cars have a vacuum operated central locking system that predates the system in your car. In the older car there is no electrically operated vacuum pump to run the locks. Instead, the Diesel models have a vacuum pump driven by the engine and the vacuum is "stored" in tanks so the locks and brakes, as well as the automatic transmission shifting controls work as soon as you get in and start the engine. In this system, the vacuum also is used to shut the fuel supply to the engine off when you turn the engine off with the key. If you get leaks to the portion running the locks, it is common to be unable to shut the engine off from inside the car, as there is no vacuum available to energize the shut off valve actuator. So, a not so unpopular solution for cheapskates like me is to disconnect the door lock system and plug the lines to restore the functionality of the key shut off device. If you do this (plug certain lines to and from the door locking system), it is possible for the trapped air volume, in an otherwise inert central locking system, to open the locks on the doors as the car sits in the sun and warms up.

So, you may have some sticking check valves or other, crimped or collapsed connectors in the system that are trapping a volume of air that the system intends to have evacuated. Once the trapped air expands due to heating, it is possible for the differential pressure generated to energize the door lock actuators. I know this is a bit of a stretch, given the symptoms you described, but I thought I would pass it along anyway.

I hope this helps, and good luck, Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #6  
Old 08-14-2002, 12:39 AM
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Quote:
Originally posted by JimSmith
Is this the only unusual operating behavior you have noted? When they unlock on their own, can you lock them with the key by turning it to the lock position, or do you have to cycle to the open position and then back to the lock position?
Well, when it unlocks itself, it's EXACTLY like you inserted the key and turned it to the left. You can go right over to it and lock it back by inserting the key and turning it to the right.

I was standing beside it once when it all unlocked and it all sounded just like it does when you unlock it normally. Seems to take about 5-10 minutes after you lock it for it to rebel and unlock.

Thanks
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  #7  
Old 08-14-2002, 01:21 AM
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I had the same thing happen to mine. I would come back to the car and it would be unlocked. Forgetting that I locked it I would open the door only to have the alarm start going off. I fixed this by simply holding the key for a few seconds when locking it in the lock position. I wait until I hear all the locks close. When you do this you can feel the weight of the mechanism "fall" onto the key. I think what happens is some part wears out and doesnt pull the mechanism down and it just goes back up but the alarm gets activated simply because the key was in the locking position. Try it, its better than replacing something needlessly
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  #8  
Old 08-14-2002, 12:55 PM
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Quote:
Originally posted by BAd124
Forgetting that I locked it I would open the door only to have the alarm start going off. I fixed this by simply holding the key for a few seconds when locking it in the lock position. I wait until I hear all the locks close.
Thanks for the input. However, in my case the locks are locking and the alarm is arming. When it subsequently unlocks itself, it takes care of the alarm too, so it does not go off when I open the door. As I said, it's EXACTLY like someone puts the key in the door and unlocks the car.

Thanks
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  #9  
Old 08-14-2002, 02:46 PM
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I was going to ask about whether it also disarmed the alarm, but you already volunteered that answer. Since the behavior is "unlocks all doors and disarms alarm", that narrows the problem. It has to be that one of the switches that detects the key turning, or some associated wiring, is bad and sending a false trigger event. From my 1986 300E, I think the that there are only two places from which you can trigger the "unlock all doors and disarm alarm" action, the drivers door and the trunk. I'd have to double check the manual to be sure, but I don't think you can do it from the passenger side door. That means you're in for some circuit chasing, but at least the number of branches is small. Or the car may be haunted. You never know.
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  #10  
Old 08-14-2002, 06:48 PM
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Locks

I had a reverse situation with my 190 D. I would get up in the morning during winter month, unlock the doors, and before I could open it, the car would lock itself. It would be funny if it wasn't so annoying. It stopped by itself in March
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  #11  
Old 08-14-2002, 07:48 PM
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Quote:
Originally posted by JimSmith
brewtoo,
The older W123 series cars ... In this system, the vacuum also is used to shut the fuel supply to the engine off when you turn the engine off with the key. ... So, a not so unpopular solution for cheapskates like me is to disconnect the door lock system and plug the lines to restore the functionality of the key shut off device.
Heh.. Interesting stuff Jim, I never knew this was the case with W123s - Neat engineering! (And end-user engeering by you..!)


brewtoo - perhaps you can disable the trunk's's 'unlock and disable alarm' switch (unplugging the electrical connection, probably) and then try the door one(s) individually. This should be the easiest way to diagnose the problem, provided there is no system technicalities that make this un-feasable.

later

Russ
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190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg
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  #12  
Old 11-16-2002, 12:19 PM
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Problem solved!

It was the little vacuum swith by the truck lock. Got weak over the years and got where the little spring would overpower it and lock the car.
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  #13  
Old 11-16-2002, 12:26 PM
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brewtoo,

Thanks for posting the results. While none of our suggestions led to the fix, it is nice to know what the problem was so we know where to look when it happens to us. Good luck, Jim
__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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