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 :smash:, 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.

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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..

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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

Wow...excellent write up. And the timing of this post couldn't be better as this is happening to me now. I did try disconnecting and reconnecting the battery and that worked...but only for a little while and I wasn't sure why it worked (I didn't know about the pump timing out).

Is there one pump that does all the pnuematics in the car? Is there anything else that I would see not working after this pump times out...or just the trunk assist?

I ask because eveything else in the car seems to work fine...though I confess that I don't know everyplace where this pnuematic system is used. And I'm concerned about this because I just did an audio upgrade and I had alot of things apart and perhaps I inadvertantly cut into an air line some place. I'm not thrilled with the idea of looking for that...so I'm hoping the fact that other things are working might tell me the problem is in the latch area this post describes and not someplace else.

Thanks for this thorough post!

There is only 1 pump that runs the pnuematics for the car. When the trunk mech has cracks and leaks air, the pump runs to long, the car senses a leak, and then trips an E-Fuse that wont allow solenoids on the trunk mech to open and close (recieving air). They instead remain closed which seals the pnuematic circuit, but won't allow it to reopen until it is reset (hince the trunk assist won't work until the system is reset, and then it will only work for a short time). Every other pnuematic function in the car will still work (seats, locks, etc.). The pump iteslf is not shut off, just the trunk mech.
I doubt you cut a line, because then the pump would continuously run and burn itself out in no time, and you wouldn't have the other pnuematic functions working.

This is why the trunk assist stops working. It is electronically separated from the pnuematic system in order to save the pump.

^Hope all this makes sense... Looks like you need to go buy some plastic epoxy and take about 30min-an hour out of your day to glue your trunk mechanism... Its an easy fix...

Nick

It does make sense...and it makes me feel better knowing that I probably didn't cut a line somewhere because everything else (seats, locks, storage latches, etc) still works fine.

But unfortunately, I don't think the epoxy fix will do it in my case. Didn't mention this is my first reply, but the other night...when I discovered this and I was 'experimenting' with how hard I had to slam the trunk to get it to fully close without the assist...I heard that dreaded, distinctive sound of something plastic breaking and moving about / falling through the interior cavity of the latch area. So yeah, I may be replacing that entire latch assembly after all. But thankfully I have your write up and pictures to get me to the point where I can pull the latch assembly and see how broken it really is. But I will have some Gorilla Glue on hand in case I get lucky!

Of course, on the other hand, my car is still under warranty. And even though something in there broke seemingly because *I* slammed the trunk, I wonder if the dealer will fix it for me? Or will he say its my fault for slamming it? Or will he see my audio upgrade and automatically tell me it must be my fault. Hmmm...I may still take a look at it before calling the dealer.

Thanks again!

A very prompt and world class response to my first post. Many thanks to Rick SL55 and NikleinR6. Can't wait to try this and report back!

And as a follow up to my last post, I brought the car to the dealer and they covered it under warranty.

Funny enough, my service advisor spent more time asking me about what components I used in my audio upgrade than he did about discussing what was going on with the trunk closing issue! :)

NikleinR6/Nick, I think you're one of my favorite posters/contributors. I am not having this issue, but appreciate your post and taking the time to write this up. Bravo!

I also absolutely love your SL.

Plus 1! What he said! This is a great tutorial and as a new member of this forum it tells me a lot about the quality of the forum and the wisdom and experience of it's members and their willingness to share. Thanks! :y

Dumb question...do all of our cars have soft close trunks? Mine doesn't seem to.

Thank you so much for the kind words....

-Nick

I am nearly positive all R230's have it, but i could be wrong.
Do this, try unhooking your rear trunk battery for about 20 seconds (remove the ground/NEG cable). Then reconnect the ground cable and softly close the trunk lid. If it pulls shut you know that
A. Your car has the soft close
and
B. You have a leak in your latch that has caused the pump to time-out in the past, and therefore trip the latch's E-fuse (which stops the latch mech. from enabling soft-close or close assist)..

Hope this helps..
Nick

If there is still warranty on the car would this be covered?

Mine was covered under the original factory warranty (on my 2007 SL550).

I did the 4 ports and it still didn't work but with looking more into it there were 6 ball bearings you kinda have to disassemble it a little bit to glue them correctly but all is good now with all 6 sealed up.
Justin

Also make sure you get a gel epoxy made just for plastic and something that is easy to work with some of the spots are tight and close to other fittings you can not get glue on.

I'm about to dig into my latch, but has anyone had any long term issues after repair? Just wondering why the bb's in the 1st place. Seems like they are designed to inhale and I'm curious if there were any side effects from sealing them.
Thanks Nik for the detailed write-up. I never would have attempted it on my own.

The bbs are there to seal the ports. When the latch is new they work quite well but as the latch housing plastic ages, the housing around the bbs cracks and leaks. The ports do not inhale. The pump will just pump air not suck it. When you glue the mechanism, you are essentially sealing cracks that have formed from use, age, and stress. Good luck with the fix. It's a piece of cake. It's been months and the mechanism still works perfectly, and I haven't reset the battery once.

Nick

Had to do this twice so far, lets see if it works this time. Located and covered the 4 holes that didnt work then with further inspection i found a total of 6 holes to glue, now its back together drying hope this works or it time for a new unit.
Justin

This should be stickied. It will help a lot of peole.

From Soft Close to Tele Aid
 

OK, finished repairing my soft close this morning - had to let the glue set overnight. Everything appears to be working as designed. THANKS NikleinR6 for your instructions! They were exact.
However when I started the car after completing the repair I got a tele aid malfunction - drive to workshop, and SOS in the left display. I don't subscribe and don't have a phone in my car. Anyone else have this issue or know how to erase the malfunction? I presume it's telling me I don't have tele aid, but I've never seen the malfunction before this. Everything else (Nav, GPS, CD) is working. Thanks.

Glad to see it worked out.

Sometimes when you remove and reconnect the rear battery the car will do funny things. One time I lost sound from the radio and it wouldn't recognize the cd changer.. all I did was remove the ground cable, wait a bit, and reconnect again. If this doesn't solve the issue let us know. There may be other steps you can take.

Mine after sealing all 6 holes is working perfect still. Thanks again for the diy!
Justin

Thanks NikleinR6 - I only removed the fuse to the pump, I didn't disconn the battery. I'll remove the ground - how long is a bit?

Also, I saw your post to repair the vario flaps, but I noticed that my "closed" sensor was a bit flat so I bent it out a little. I'm crossing my fingers, but it's tight. It used to fall every time the trunk lid was lowered and adjusting the screws was no help. Lowered the roof several times today - no issues.

Rob

Tele Aid Malfunction
 

Disconnecting the ground (1/2 hour) did not reset the tele aid malfunction. Any other suggestions?
From googling, seems like this is a very common problem with all mb models, but most either live with it or take it to the dealer. Just can't figure out if it's related to my soft close fix or a coincidence.
Thanks.

Other two ports
 

For those of you who are looking for the other two ports that need to be sealed. Here is a picture of them. They are very hard to get to but using a bent peice of wire to apply the glue it is possible.

Thanks for the tips, Nick. Looks like the latch is almost identical on a W215 CL.

Just a note for everyone else, if it trips the breaker when you close the trunk, the problem is one of those ball bearings or a leaking hose. If it trips the breaker when you open the trunk, it's the bladder/actuator (small hockey puck looking thing attached to the latch). This piece is inflated and then the bladder actuates the unlocking mechanism (this is the worst engineering imaginable).

You need to remove the puck (it is secured with two round prongs, which you push back through). Then take it apart to see how it works. You need to epoxy this back together around the "hemisphere." Use some JB Weld, caulk it up, put it back together, and then clamp it together until it dries. That should hold it.