Phat_J

Hey all,

So I had an issue with the soft-close feature not functioning on my 2015 C400, I fixed it, and decided to make a guide for it in hopes of helping others. There's a pdf version of my guide attached to this post too.

The issue. Power assist trunk / boot does not fully shut, leaving this unsightly gap:



Thanks to this post for the picture:
https://mbworld.org/forums/c-class-w...t-problem.html


The likely culprit. This motor is engaged when the trunk/boot lid has finished closing, and pulls it fully shut:





Here is how to diagnose and replace that motor.

This guide is for the W205, but many other models use this same motor
(https://www.autohausaz.com/pn/MB-2047500060)



Tools needed

- Replacement motor (I found mine on ebay, part number A 204 750 0060 / A2047500060)

- Trim removal tool

- Torx screwdriver

- Needlenose pliers

- Flashlight

- Multimeter and some spare wire (optional)





1. Remove lower edge of trunk

a) Remove plastic rivets




I found this to be the most difficult part. I pried the rivet a bit with the trim removal tool, once they were partially extracted, I used needlenose pliers to grab them and pull them out.

b) Once the 2 black rivets are out, pull up hard on the trunk piece and it will pop out. There are 4 white rivets that hold it down.






Now you can see the mechanism that gets pulled by this wire encased in foam. The wire leads to the failed component that we'll be replacing.






2. Gain access to behind the trunk lining

a) Remove the tie-down latch with torx screwdriver (plastic top easily pops off)





b) Remove plastic hanger/fastener









c) Pull back on trim to reveal motor unit. You may have to use a trim removal tool to pry it free.




d) The motor is contained in a plastic and foam enclosure held on by an orange rivet

e) The enclosure can slide to detach from the orange rivet. I also detached the power cable.









3. Diagnosing, testing for power:

At first I wasn't sure if the motor was faulty, or if it wasn't getting power to do its job. Or, the cable may have become dislodged over time. Skip to step 4 if you want to just replace the unit without testing it.


a) The motor unit is in a foam enclosure held on by an orange rivet, you should be able to pull up on the unit and it will release from the orange rivet. Then you can pry out the orange rivet with a trim removal tool.




b) Disconnect the power cable.






c) Fold down the right rear seat.



d) I’ll be running some wire from the power cable to my multimeter, so I can read the multimeter from the back seat while the trunk closes. I connected some wire as shown to the trunk motor’s power source, and ran it to my multimeter.






e) As the trunk closes, watch for the multimeter to show 12 volts. This means the soft-close motor is getting power to perform the soft-close. Now we know it must be a faulty motor, assuming the cable running to the latch is attached properly.

https://streamable.com/4vnlvn



4. Remove and replace the faulty motor.

a) The motor unit is in a foam enclosure held on by an orange rivet, you should be able to pull up on the unit and it will release from the orange rivet. Then you can pry out the orange rivet with a trim removal tool.




b) Disconnect the power cable.



The “ball bearing” end of the wire detaches easily from the unit, along with the blue piece holding it in place




b) Attach the cable to the new motor (the cable should wrap around, and the blue piece should snap into place as shown)




c) Connect the power cable and seat the motor into the plastic and foam enclosure

d) Pry the orange rivet out from the frame of the car, attach it to the motor enclosure, then push the motor unit with the rivet back into the frame. My apologies for not taking a pic with the rivet seated in the motor casing, but hopefully it’s intuitive. Red arrow shows where the rivet should go.





5. Test it

a) Make sure none of the trim you removed is in the pathway of the trunk closing

b) Close the power trunk and see if it fully soft-closes. Please excuse the dirty car

https://streamable.com/mx5i96


6. Re-install trunk lining

a) Make sure the lining goes fully under the rubber trunk trim

b) Re-attach the hanging clip, the tie-down latch, and plastic covering

c) Re-attach lower edge of trunk, make sure all 4 rivets click back into place

d) Make sure the rubber trim is over the edge of this trunk piece. I used a trim removal tool to run along this edge.




e) Re-attach the 2 plastic rivets into the trunk piece






Done!

SorinMB

Dunno if its bad luck but i got mine off some spare parts, tested and worked, 2h later doesnt work

I need a new part

Penguin123

With your impeccable instructions, I was able to fix this effortlessly. You shine like a star and embody true kindness, sir, for graciously taking the time to provide such detailed guidance. I am sincerely grateful to you, thank you from the bottom of my heart!

Phat_J

You're very welcome! Glad I could help

rxm00

Thank you for providing this tutorial.

My boot has also recently been experiencing this issue with it not being closed entirely. I do not have a multi meter to test but I’m just going to guess it’s very likely to be the same culprit.

I have just had a visual look my motor and I can see it looks like the following image you provided, and doesn’t wrap around:


What mine looks like currently

Now, was it like this for you? The original part not being wrapped round like the following image?:


Should it look like this and the cable be wrapped around?

I have found a second-hand motor like pictured above with the cable looking like it will be able to be wrapped around:



So, do you know if the one above will likely work just by looking visually? I’m trying to understand whether the fact that when I look at my current motor the cable doesn’t wrap around, is this the problem? Baring in mind my boot is open so I don’t suppose that’s why it isn’t wrapped when I have had a look, or whether the motor just doesn’t work. If you can advise it will be much appreciated.

Phat_J

It's hard to say if it's not functioning from just seeing the picture. Can you turn the motor at all by hand, and put it into the position like my picture?

rxm00

It’s hard to turn by hand but I managed to turn it so it is like the one in your picture where the cable wraps around, however, when I close the boot doesn’t latch on at all and therefore doesn’t close. With every close/open cycle the motor goes lower and lower back to the original position as shown in my first image. Does this show that the motor is knackered and not working? As my guess is that it doesn’t seem to engage and wrap the cable back round when the boot is fully closed which i guess would be the motor ‘vacumming’ the boot closed.

What would you say to this? I might just bite the bullet and purchase a second-hand working motor? Thanks in advance

Phat_J

I would say just order a replacement part instead of messing around with this.

rxm00

Hi @Phat_J . I just received my second hand motor with same part number and attempted to fit it. I followed all steps and wrapped the cable round, clipped it in place and connected the wires back up and when i close the boot this motor does not engage at all and does nothing. The cable being wrapped round is the motor already in the closed position where it ‘vacuums’ the boot shut and therefore when i press the close button for the boot it doesn’t close as the latch is too far down. But the motor just doesn’t move at all for it to be in the open position. If I push the boot down once it does lock all the way and the panel gap is perfect as it would be if it ‘vacuums’ shut but when i open the boot again the motor just doesn’t engage to release the lock on the cable upwards.. any ideas?

Vins

This is absolutely fantastic person guys! I must send my appreciate from Australia. You make this job so easy. Thank you so much