The brief
The S350L had a power window stuck, not moving up or down, with a noise from inside the door when it tried. He brought it in. A window jammed shut or down is awkward, and on a flagship like this it's the kind of thing you want fixed properly with the right parts. That door has the window motor, the electric motor that drives the glass, and the window regulator, the mechanism that carries the glass and moves it up and down on its rails. Both wear, the motor's brushes and gears strip so it stops turning or strains, and the regulator's cables fray and plastic guides crack so the glass loses support and jams. On this door both had reached that point, so both needed replacing with genuine Mercedes parts.
The diagnosis
The door card came off and it told the story: the window motor worn and not driving, and the regulator with a frayed cable and cracked guides, the glass no longer properly carried, which is exactly why it jammed. The wiring and the switch checked out, it was the motor and the regulator. That's a motor and regulator replacement, complete assemblies rather than repairs, with the glass realigned afterwards.
The work
The door card was removed, the failed motor and regulator taken out, and a new genuine Mercedes-spec window motor and regulator fitted, the glass clamped into the new carrier and aligned so it runs square in the channel. The window was cycled up and down to set its stops, and the door card refitted. A check confirmed the window ran smooth and quiet through its full travel and held its line top and bottom.
The outcome
A window that runs smoothly and quietly, no jamming, no noise, sitting square and sealing properly. The S350L went home with the window sorted. A failed motor and regulator only get worse until the glass is stuck for good, so changing both assemblies with genuine parts and realigning the glass put it right.
