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Have Trunk Soft Close / Trunk Assist problems. Here is how to fix DIY.

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Have Trunk Soft Close / Trunk Assist problems. Here is how to fix DIY.

 
Old 06-16-2010, 08:48 AM
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Have Trunk Soft Close / Trunk Assist problems. Here is how to fix DIY.

A common problem on many of our cars is the the trunk assist will randomly stop working one day, and you won't know why. You can unhook the convenience battery and reconnect, and the soft close function will begin to work again, but not for long. Eventually it will stop pulling the trunk closed again, and you will have to pull the fuse (or unhook the battery). This is only a temporary fix which could ultimately result in pump failure.

The problem with our cars is that the soft close latch is operated by air, and if there is a leak anywhere in the system, the pump times out, and the soft close function ceases to work until the system is reset.
So, on the latch mechanism, there are 4 air ports that mercedes plugged with small ball bearings. These bb plugs work fine when the latch mechanism is new, but as the plastic around them ages, it cracks where these ball bearings are. The cracks allow air to escape, and here is the problem.
The solution is to buy some $5.00 plastic epoxy, and glue the outside of the ports and the inside of the ports shut.
You will notice some orange silicone on the latch assembly. I initially tried to use silicone gasket maker to cover the ports, but quickly found out it was not strong enough , and the air pushed its way out. So make sure you use a strong plastic epoxy. Gorilla Glue makes a great gel (super glue) epoxy. I used it later...

In the next series of photos i will show you how to resolve the problem permanently.












After you pull the latch mechanism out reset your convenience battery, push the latch clasp in 1 click, watch as the pump actuates and closes the clasp fully, and LISTEN FOR AIR ESCAPING.. When you find the air leak, begin applying the glue there, but also apply it to the other ports just in case. Be generous..









You could take your car to the dealer and pay over $300+ to have a new latch installed, or you could fix it like i did in less than 30min and for less than $5.00

Last edited by NikleinR6; 06-16-2010 at 08:51 AM.
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Old 06-16-2010, 11:22 AM
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Don't spare the epoxy. The cracks can propagate up the tubes over time. You need to pull your fuse or disconnect the trunk battery to get the system to reset.
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Old 06-16-2010, 12:58 PM
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Thank god for my Chrysler warranty that replaced mine.

Great DIY!
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Old 09-15-2010, 11:34 PM
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Excellent post! How long should you hear the air pump run after the trunk is shut? Just completed this fix and it is working. Unknown for how long it will work because I hear the air pump running for at least 3 seconds after the trunk is shut. The trunk assist is now $400 plus, just for the part. Thanks again for this post!
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Old 06-16-2011, 01:18 PM
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Originally Posted by busaboy View Post
Don't spare the epoxy. The cracks can propagate up the tubes over time. You need to pull your fuse or disconnect the trunk battery to get the system to reset.
can anybody assist with exactly where the fuse is located for the trunk latch mechanism? TIA. AL
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Old 06-16-2011, 02:31 PM
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E 63 Renntech, E55 Renntech, SL65, SL 55 030, ML, bunch of old ones--they come, they go...
It's in ....

the aux fuse box in the rear storage compartment, behind the passenger compartment. A little bit of a pain to get to, you have to pop the cover up from the bottom , which is most easily done by removing the little front dummy trim panel. I believe it's the fourth fuse in from the left, if you're looking from your passenger seat towards the rear (which you will be, cause you're top won't go down). I believe it's a yellow 20A.
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Old 06-23-2011, 12:44 PM
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Originally Posted by allenjdmb View Post
the aux fuse box in the rear storage compartment, behind the passenger compartment. A little bit of a pain to get to, you have to pop the cover up from the bottom , which is most easily done by removing the little front dummy trim panel. I believe it's the fourth fuse in from the left, if you're looking from your passenger seat towards the rear (which you will be, cause you're top won't go down). I believe it's a yellow 20A.
thank you very much for this info. the diy epoxy fix and fuse reset has been done and my trunk soft closes perfectly well for now =)
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Old 07-08-2011, 09:58 PM
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E 63 Renntech, E55 Renntech, SL65, SL 55 030, ML, bunch of old ones--they come, they go...
Oh well....

didn't work for me. Still stops working for no apparent reason. I wonder if I have a defective latch. It won't work from time to time when I grab the rear lever. When it stops working, the trunk open light on the door switch is on. I have reset the fuse maybe a dozen times, but even after this fix, it continues to malfunction. Suggestions? Thanks...
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Old 02-09-2013, 12:29 AM
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Thanks so much for this very well done DIY. I now have trunk closure assist. First time since I bought the car!!

Cheers!
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Old 02-09-2013, 01:36 AM
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i did it too, and trunk working great now still. just an fyi, don't use orange high temp silicone as you will get it everywher. just use regular clear. lol
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Old 01-18-2014, 04:00 PM
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I just finished this repair a few days ago, and the system seems to work GREAT now. THANKS to all who added comments, but especially to NikleinR6 who did it originally and posted such great suggestions.

I highly recommend his suggestion of Gorilla Glue epoxy for this repair. It has low viscosity when first prepared, so flows around the cracks/BB's readily. I found it was better to plan on doing two of the repairs at a time instead of all 6, that way I could hold and rotate the motor in a way that the low viscosity epoxy didn't 'run all over'. I also applied a small vacuum into the motor with each seal I was doing (I used a mighty vac, but I'm sure good old mouth suction would probably be enough if done early while the epoxy is very fluid). This really should seal everything very well and permanently, as a small amount of the epoxy is pulled into any crack.

One other thing I'd suggest - before you start to remove ANYTHING, raise the trunk as if you are putting the top down. The 'flaps' then will uncover the two fasteners for the trunk liner, and you can easily remove the center pin from each one. This will make it much easier to get the trunk liner down when you've removed all the mechanical stuff and are ready to take the vacuum motor out. You then 'close' the roof to get the trunk closed and start the procedure.

Obviously When everything else is done, you reverse the process to put the liner back up into full position where the flaps are. Push the fasteners VERY hard to get them and the liner fully in position and re-insert the two center pins for those fasteners. You can't get to these with the trunk hinged at the front.

By the way - if you break any of the plastic the fasteners they are available at MB dealers, but VERY expensive!

Gary Knox

Last edited by kittyandgary; 01-18-2014 at 04:05 PM.
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Old 07-18-2014, 06:05 PM
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I'm about to attempt this but my question is wouldn't nipple caps work just as well and easier to install?
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Old 03-10-2017, 12:27 PM
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Old thread but thought I would post here..

My brother recently helped me with my 2007 SL55 with this soft close option. He took out the latch and sealed up every potential leak. Took his time and made sure each one was completely air tight. Since this has been done, my trunk closes perfectly. Did it 10 times in a row and last time I took it out, no worries. This thread is what helped out in a big way.

Cheers!

Shaun

P.S. At the Dealership, they told me it was the pump and it was a $2,000 fix plus labour. It just seems Mercedes won't admit this part is not very well engineered and forums like these really work.

Thank you
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Old 09-03-2017, 10:48 PM
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I had this issue. Purchased the car with the salesman slamming the trunk to get it to close. I wasn't sure I was on the right track here because when I would operate the truck handle the actuator would move. Several things happened Actually so I thought the assemble may be working hit something else was wrong. When I remove the fuse to reset the system though it was clear that the soft close feature had timed out. It worked again for one cycle and then stopped again. I could here air leaking around the assemble as is the case in this thread. I sealed everything with JB Weld. I did find a 5th ball bearing on my assembly that I sealed as well.
Fixed the issue for me and who cares if there is some sealer on it you will never see it hidden in the trunk.
Really no need to buy a whole new unit that will fail in the same way.
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Old 12-06-2018, 09:52 PM
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I just finished epoxying the 6 valve ends on my 2003 SL55AMG truck latch. Iím going to let it dry overnight and install it tomorrow. Thank you so much for the excellent tutorial. Very easy to follow.
I have high hopes and will let you know if it works.
Thanks again,
Wm

Used J-B Weld to epoxy ports
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Old 04-04-2019, 11:44 AM
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will this work for CL55 amg trunk acutater?
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