95 w124 pass door lock issues
 

Got a wierd issue with the pass door lock. Been doing some engine work so the battery has been disconnected the pass door can be locked manually but will slowly push its way back up. I had the door apart and didn’t see anything out of the ordinary. With the battery connected everything seems to work normally. Is there a check valve or air in the lines causing the lock to pop back out?

Looks like you nmay have catched a vacuum pipe . These are the small bore nylon pipes that run around the engine . Any vacuum leak will play up with the door locking system.It wont work without the battery to power up the vacumm pump that sits .. in the rear under back seat You can get a Mighty Vac to test the vacuum. The door lock pins should stay down after you lock it .

W124 central locking runs off an electric pump under the rear seat. The system is isolated from engine vacuum lines.

This is a stretch but maybe there’s a leak in that door’s actuator. With the battery connected the pump can run a full cycle and lock the door. But if you disconnect the battery before the pump runs a full cycle, you catch the actuator before the door is fully locked.

Listen closely at that door when locking. Do you hear a hiss?

Remove the rear seat and take the central locking pump out of its foam cocoon. How long does it run when you lock or unlock? It should only run 3-4 seconds with tight plumbing. It times out after 30-45 seconds if there’s a leak.

Sixto
98 E320 wagon
02 C320 wagon

When you don't have the battery connected, the vacuum hose is in a 'pressured' state when the door is locked manually, so it may slowly pop out. If battery is connected the vacuum hose would be in a vacuum state when locked. Everything is normal.