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'84 300DT, '97 S320
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682 Posts
Discussion Starter · #1 ·
I thought the general rule for the system shutting down this feature on any given door was 2 closings in a row that take 10 secs. This started happening last week. Happened a couple of more times. Decided to listen to pump a count seconds.

2 days ago, got in car to go to work. Closed fine. Didn't count the sec's.
After work, it wouldn't work. Pulled fuse, worked.
Got home, turned off car, and opened and shut door 5 times.
Each one of the pressure part was about 5 sec's, then the vacuum part.

Next morning, get in car, door auto-closes fine, took about 9-10 seconds.
Got to work, wouldn't work.
So, I only got 1 strike instead of 2.
After work, pulled fuse, door works, tried 4 times, all about 5 secs.
Got home, still worked, about 5 sec's.


If a hose were going bad, I'd think it would always take the max time, 9-10 sec's, but it still often takes just 5 sec's. It could be temperature related - we've had some pretty good temp swings lately.

Oh well, more to come later, I'm sure.
 

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1995 Mercedes-Benz S420 (W140), 1997 BMW 740iL (E38), 2011 C300 Luxury (W204)
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1,314 Posts
I found that my car does this randomly as well. Sometimes one will just decide not to work anymore. But after fuse pull, it can work for months. The one day it will screw up again. Something I decided to live with. One theory I had was if I had a lot of passengers, say 4 people. We all close doors same time, maybe that kinda screws the pump up due to so many at once. But then again I was never able to successfully reproduce the problem.
 

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1994 S320, S 600 1994 , 1993 400 sel , 1995 S500 SL 600 1999
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475 Posts
my car driver door has started with the same problem,
it closes with a tick noise & then releases it again,
1 out of 100 it fails & when the front door fails all the door fails 1 by 1,
what should be the problem here?i dont like too have a imperfect car,
is it the vacum pump?
 

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W220 S320 CDI 2005; W140 S280 1994 (Sold Nov. 2012)
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867 Posts
I found that my car does this randomly as well. Sometimes one will just decide not to work anymore. But after fuse pull, it can work for months. The one day it will screw up again. Something I decided to live with. One theory I had was if I had a lot of passengers, say 4 people. We all close doors same time, maybe that kinda screws the pump up due to so many at once. But then again I was never able to successfully reproduce the problem.
I currently have the same problem - but only with the boot (trunk) - never with any of the doors. I adjusted the pressure switch contacts on the pump unit - which helped a lot - but didn't get it quite right, so I also live with it pro tem: it fails about once a fortnight.

I have considered whether it's worth cleaning the pressure switch contacts, as oxidised or pitted contacts could certainly lead to unreliable/variable switching characteristics. But, while I'm sure that ambient temperature/pressure could have a small effect on the pump performance, like dirty switch contacts, it would surely affect all doors and boot the same, not just pick on one of them. I wonder whether the neoprene bellows in the actuators can finally start to go very slightly porous and whether, in the early stages, this porosity can be variable. Dunno.

Mike
 

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140 600 1991
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221 Posts
Maybe the microswitch that sends signal to the pump fails sometimes? Driver's door is the most used (usually) = normal for dying first.
 
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