S420 rear trunk assist wont work - PeachParts Mercedes-Benz Forum

greasybenz · #1 02-25-2007, 09:53 PM

Sorry if it has been discussed before but i cant seem to find an answer through search.

The rear trunk wont come down, the handle goes in but i think its electronic not vacuum? All the doors still have the close assist working only the trunk has the problem. Where to look?

help much appreciated

greasybenz · #2 02-26-2007, 03:08 AM

bump

wbrian63 · #3 02-26-2007, 09:40 AM

The trunk pull down system combines work from both the pneumatic accessory pump (under the passenger rear seat) and the closing assist pump (in the trunk on driver's side up next to the gas tank).

The handle is extended/retracted by the pneumatic accessory pump.

The pull-down mechanism is extended by the pneumatic accessory pump and retracted by the closing assist pump.

When the closing assist pump is called on to do its duty by a door being closed or the trunk being closed, it applies pressure to the required line for a specific amount of time. If the circuit operates properly (meaning pressure is being held), then the cutoff limit for that circuit will be reached and the pump will cut off. If the cutoff limit isn't reached in a specific amount of time, then the pump turns off anyway and makes a "note" that the specific circuit failed to reach cutoff pressure. It will only allow this problem to reoccur a certain number of times before it cuts that circuit out of the loop entirely.

If your door closing assists are still working fine, then likely the pump has taken the trunk close assist out of the loop. If your door assists aren't working either, then possibly they've also been removed from the list, or the pump itself is not working.

To get the trunk "back in the loop", pull the fuse for the pump for about 5 or 10 seconds. It should be in the fuse box in the trunk.

If that fixes the problem, then you need to check to see why that circuit isn't reaching cutoff pressure - possibly a leak in the hose, or in the mechanism that actually pulls the trunk down.

It's also possible that the pump is too sensitive - mine tended to run too long after closing a door or pulling the trunk down, so I adjusted the cutoff pressure and fixed the problem. There's an excellent article to be found at www.uberalles.com on how to adjust the pump to reduce the number of timeout errors.

In the meanwhile, you can manually retract the pulldown hook. There are two levers visible under the trunk lid - push one to release the hook and pull the other to retract the hook, then release the first one. Then the trunk will close in a normal fashion - that time only. The next time you open the lid, the pneumatic assist system will extend the pulldown hook again.

Hope this helps.

greasybenz · #4 02-27-2007, 01:29 AM

thank you!

I had forgotten that removing the fuse for some seconds and putting it back in might make it work. Someone had taught me that at one of the gtg's on a W140 diesel.

Im going to try pulling the fuses.

thanks again.

will70724 · #5 03-11-2007, 06:51 AM

Where are these manual trunk levers to manually shut the drunk? I cant get my trunk to shut, and I dont see these levers anywhere? Thanks.

JimF · #6 03-11-2007, 12:16 PM

Quote:

Originally Posted by greasybenz

The rear trunk wont come down, the handle goes in but i think its electronic not vacuum? All the doors still have the close assist working only the trunk has the problem. Where to look?
help much appreciated

Check out MENU#28 to review some repair techniques. . .

greasybenz · #7 03-12-2007, 02:15 AM

well i pulled the fuse for the close assist (located in the trunk on the passanger side) and it wasnt burnt so i had it out for 10ish seconds. Put it back in and like magic it closes again!

will70724 · #8 03-12-2007, 02:42 AM

I take the fuse out. the trunk interior light goes off. I wait a few mins and then put t he fuse back in the trunk light comes on. I hear the pump powering up. but nothing happens, when I shut the trunk nothing. Wont latch wont close nothing. When i push the trunk latch that holds the trunk shut down the trunk light goes off and i hear the pump powering up and then at the end a hiss.

but no matter what I do I cant get the trunk to shut.

What would you guys recomend because I cant make it to the shop til thursday ( 4 days from now)

greasybenz · #9 03-12-2007, 03:25 AM

My guess is a vacuum leak. But let me understand what your saying. So if you shut the trunk lid it wont hold down closed?

On my S420 the trunk lid will close but wont be pulled down to be flush. After pulling the fuse the pump worked again and pulled the lid down to be flush with the rear panels.

will70724 · #10 03-12-2007, 04:06 AM

Nope nothing, not close mostly but just wont tighten. Im talking if i shut it and let go the trunk pops right back up. Wont shut at all nothing.

What can I do ( i have already replaced the fuse, and took the fuse out for a while to see if that worked)