Hi, the problem is usually a faulty trunk lock mechanism. The vacuum actuated trunk release mechanism leaks and will not open the lid. You will need to have the complete lock replaced as there are no serviceable parts to the lock.
It is #10 in the image above.
You can try removing fuse 62 in the rear fuse box for a few seconds and reinstall it and see if it resets the PSE module. Sometimes that will get the trunk working again but it will usually be a temporary fix if there is a leak in the system.
Let me know if you have any questions.
On my 2002 S55 AMG U can't open my trunk with the remote key or inside with the door release, what could be the problem?
Just read the above, thanks
Let me know if you need anything else.