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Delay in trunk opening when cold

5424 Views 11 Replies 2 Participants Last post by  c180w20294
The nights here in the Bay Area are getting cooler and my car is parked outside. Every morning when I unlock the car with remote, all the doors are unlocked right away except the trunk. It takes 40 seconds or more for the trunk to get unlocked. All this while I can hear buzzing noise from the trunk and finally it opens. The switch on the console does not help either. After I have driven the car, everything works fine.

I drop my son and his friends to school every morning and they put their bags in the trunk. I am scared that some day I will take them to school and the trunk will not open and they will not be able to get their bags.

Any idea on what is going on? Also if the trunk does get locked is there any way to force it open?

Thanks for your help.
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Should the central unlocking of the trunk ever fail; make sure that you can open the trunk with the metal emergence key blade as illustrated below.
The emergency key blade is housed within the remote fob and is released by moving a lever to the side on the top of the remote fob.

Flood the trunk lock twice a year with WD40 or Penetrating oil, have the trunk lid fully open when you flood it with oil to allow the oil to get down into all parts of the lock, see Pic12 below.
Replace remote fob batteries if this hasn’t been done recently.

Ideally, the vacuum pump, located in the trunk, shouldn’t run for more than 2 or 3 seconds, any longer then there is some kind of fault.

If you press the trunk open button on the remote fob, for 2 seconds, will the trunk spring open regardless if it is hot or cold?
Does the vacuum pump run continuously for 40 seconds?
Does the fuel flap also unlock immediately just like the doors?

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As the key blade won’t turn in either direction then the lock is seized.

Make sure the key blade goes fully into the key hole, if you aren’t sure; compare how far the key blade will go into the glove box key hole or the driver’s door key hole.

Open the trunk lid fully and squirt/flood with WD40 or Penetrating oil into the key hole through the Red aerosol straw, Pic 12 above, push the key in and out of the lock and turn it side to side as much as it will go. Keep trunk lid fully open for 20 minutes to let oil spread down throughout the lock, repeat above every couple of hours.

Don’t use force with pliers to turn the key blade, you can use finger force if the key is equipped with a key ring as illustrated in pictures above, you will get a better grip on the key if there is a ring on it.

The use of the emergency key blade to open the trunk is purely mechanical, there are no electronics involved, the vacuum pump, remote fob or switch inside car play no part in unlocking trunk with the key blade.

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However, I am not sure if the following is normal.

1. When the car is centrally locked with the remote fob and if I use the metal key blade to unlock the trunk, all the doors also get unlocked and all the four windows roll down half way.

That’s not normal, is the alarm system in working order, test it, see second post here… W202 - How to test car alarm? | MBClub UK - Bringing together Mercedes Enthusiasts
When the car is locked with the remote fob, then the car alarm is armed, if the trunk is then unlocked with the key blade and the trunk lid is opened then the alarm should sound and the hazard lights should flash. A faulty alarm could be causing this window opening fault.

2. When the car is locked and I use the remote fob to to unlock the car, it still takes some time for the trunk to get unlocked before I can push the keyslot button to open it. Before it was never a problem.

The vacuum pump should not run for more than 2 or 3 seconds, no mate if you push inward the trunk lock or operate the lock or unlock buttons on the remote fob. How long exactly does the vacuum pump run for when you unlock or lock with the remote or when you push inwards the trunk lock?

3. If the car is locked, the trunk open button on the remote fob does not always work and when it works, it takes a long time to open the trunk

You have keep pressed the trunk open button, on the remote fob, for 2 seconds, how long does the vacuum pump run for when you do this?

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Not heard of all the doors getting unlocked and the all the windows roll down resulting in the use of the key blade, very strange.

The whole idea with the emergency key blade is so that the trunk can be opened without battery power; it is a purely mechanical action when you turn key counter clockwise and push inwards on the lock.

There must be something wrong with the vacuum pump, you could try unplugging all 4 electrical connections to the vacuum pump for ½ an hour and then reconnect them all, this might reset the vacuum pump.

In the video below is a very similar vacuum pump from a w208, as an example, no need to undo the Yellow tubes, just the electrical connecting plugs.

Check each electrical connection for corrosion/damage and remove the cover to reveal the pumps PCB to examine it for corrosion/damage, below is an earlier version of your pump to show how to open the cover for the PCB.

One other question, is the alarm siren the original unit or was it ever changed in the last 18 years?

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It could be related, those sirens all give trouble after 10 or 12 years, if it’s the original, then its 18 years old now.
The siren contains the alarm system, being associated with locking; it’s involved with the vacuum pump. The internal rechargeable batteries eventfully fail and damage the alarms circuit board and can cause all types of weird faults, and your window opening fault is quite weird.

If I were you, I would unplug the alarm siren, and keep it unplugged until you get to the bottom of this problem, if there is no change in the problem when you unplug the siren, then try, as suggested, and take a look at the vacuum pump.

See also…

The alarm siren is located behind the right front wheel arch liner in picture below.


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