2003 S600 - as I try to sort out several issues with my S600, I've decided to tackle the trunk issues. After some time where the trunk would only open half-way (at best), it's topped working altogether.
I opened the trunk today, and removed the covering from the lid. I removed the pump from it's location next to the battery. The fluid is visible in the opaque reservoir and appears to be between 1/3 and 1/2 full. With the trunk open, I can hear the pump running for 15-20 seconds, but there is no movement of the trunk.

Can someone provide some details on the trunk operation? I had hoped to trace the hydraulic lines to see if I see any evidence of a leak, but haven't yet removed all of the interior coverings.

I've tried to reset the system by holding the door-located button, and removed and replaced the fuse. I've also searched the forum - lots of amazing information related to specific issues, but I haven't found exactly what I'm looking for.

Thanks in advance

 

So far, I have not found any way to reset the PTL (Power Trunk Lid) other than by using SDS.

"Normal" operation on my 2003 S500:
Powered OPEN is possible with the button over the license plate; or by pulling the trunk button on the driver's door down for three or so seconds (time delay is adjustable); or by pushing the trunk button on the key fob. The PSE (Pneumatic Service Equipment) unlocks the lid pneumatically, then the hydraulic pump starts running, and the lid opens to the fully vertical position. The hydraulic pump runs for several seconds after the lid is fully open.
Powered CLOSE is possible with the button on the bottom edge of the trunk lid; or by pushing the trunk button on the driver's door in for three or so seconds; or by pushing the trunk button on the key fob. The lid on my car closes surprisingly quickly (it startles most people who see it from a close distance). The lid is firmly shut hydraulically - there is no "soft-close" action. The hydraulic pump continues to run for several seconds after the lid shuts.

If the PSE doesn't unlock the trunk, it can't open. You can try resetting the PSE system. Go to the right rear passenger area, and find the floor lamp located behind the passenger's heels. Pull the bottom of the lamp housing out of the carpeted wall, then push the housing down to release the top. Move the housing out of the way - no need to disconnect it. Look at the row of fuses now exposed, and find the yellow 20-Amp fuse near the inboard end of the row. Pull it out, and make sure that it isn't blown - if it is, replace it with a high-quality 20-Amp fuse. Removing and reinserting the fuse resets the PSE system. See if the tunk now opens at all.

The hydraulic lines run to the right trunk hinge area. I doubt that leakage is part of your problem.

 

Wallyp - thanks for your response. Unfortunately the trunk won't move in either direction regardless of whether I use the door button, trunk button, or key fob. I did pull and reset the PSE fuse today without any change (checked for continuity before replacing). The fact that I can hear the pump running makes me think it's not a fuse issue. If the weather holds tomorrow I will remove the rest of the trunk liner and see if there's a hose kinked that's preventing the movement. Beyond that, I might try to top up the fluid, but otherwise I'm out of ideas.

 

Start with fluid level...that's the first thing with hydraulic systems. IF it's low, correct it and then chase down the leak. I don't have the system, but that's where I would start..

 

Most likely just low on fluid if you hear the pump