JBware

Hello MBworld Family,
I have an '05 S500 with a defective trunk assist. It does unlock but doesn't lift. Also, the trunk close button doesn't work. My plan is to check fuses, then check the hydraulic fluid in the pump. Am I on the right path??

Jack_88

Yes, you are on the right path. Let us know what you find.

tusabes

Not all s500 have the power trunk lift
Some just have power unlock

You can tell the difference if the lid has gas struts or springs . Lids with gas struts have the power trunk lift/power close

Lids with springs only have power unlock

JBware

Ok, I checked and the pump has plenty of fluid. The is a set of struts on each side of the trunk lid and they have a great amount of tension. I also read in a separate message forum that there might be a motor somewhere that controls the trunk assist. Could this be what the red auto close button is controlled by?

ItalianJoe1

The pump has a small ram on the right, above the pump, that raises and lowers the trunk. The two struts you see are to support the lid, not move it.

Check power to the pump if it's not out of fluid. My car leaks profusely from the ram seals, which are not serviceable according to MB. Rather than buy a new pump/ram unit, I'm gonna pull it and send to TopHydraulicsInc for a rebuild.

JBware

Thanks for the info. I'll do some more digging and see what I find.

tusabes

This is the trunk lift pump and the hydraulic ram is the long horizontal Rod

JBware

Thanks for the picture!!!

eldos1

Also, My 06' trunk has a delay with remote or trunk button. It unlocks first, then a second push will get it to rise. If the car is locked, then you can get it to unlock and raise with remote with one push.

I had trunk lid problems and it was related to the hinges getting stiff from lack of lube. Incomplete opening is a sign of this.

I just thought I would throw that in here as old threads still get looked up from google.

wallyp

I'm not familiar with the power lift on the trunk (boot) lid, but on the standard trunk opening button on the driver's door, there is a programmable delay between push and unlock.