1991 Mercedes-Benz 420SEL Window Regulator Replacement Cost

Window regulators are not a consumable item, but they do wear out. It is not uncommon to replace a regulator in a car with 100,000 miles.There is however no recommended frequency of replacement.

A failing window regulator is diagnosed by actuating the window motor switch (or window crank in the case of a manual regulator) and observing if a) the window regulator motor is working; b) the window is travelling smoothly in its tracks; c) the window is travelling fully from top to bottom; d) the window is tight or loose in its opening. If the regulator motor is not working, a technician might first check for a blown fuse or faulty window switch. But if the regulator motor is working and the window is not moving smoothly, or it is not travelling all the way up or down, or it is loose in the opening, a technician will remove the interior door trim panel to look inside the door and verify that the regulator is broken.

Replacement of a window regulator depends on the type of vehicle and style of regulator. In general, a technician will remove the interior door trim panel, taking care not to damage the latch cable or any electrical wiring that is attached. Next, the door vapor barrier is removed. The window is disconnected from the regulator (this may be difficult if the regulator is not working at all) and removed from the door. Finally, the regulator is removed from the door and (in the case of a power regulator) the regulator motor is removed from the old regulator and installed on the new one before reassembly.

RepairPal recommends that a repair manual be referenced before removing an interior door trim panel to prevent damage to the retaining clips, electrical wiring, and latch cable. Also, if a power window regulator is broken but the regulator motor is still operational, it may be possible to transfer the motor to the new regulator (this is not possible on some vehicles as the motor and regulator are integrated).

When replacing a window regulator it is important to be aware of any electrical wiring that might run between the interior door trim panel and the door shell. It is easy to break sensitive electrical connectors when removing the trim panel. There is also a door latch cable that needs to be removed; the cable can break if care is not taken when removing the trim panel. The panel is held on to the door in most cases by screws, bolts, and plastic clips. These clips are "blind" - they cannot be seen from the outside of the trim panel - and in some cases are "one time use" fasteners. Some manufacturers require a reset of the electronic module that controls the windows after a regulator has been replaced. On some vehicles, there is an airbag mounted behind the door trim panel. Naturally, extreme care should be exercised when working around Supplemental Restraint System (SRS) components.

In most cases, a DIYer with intermediate experience can complete this repair. The level of difficulty depends on the make and model of the vehicle and the condition of the window regulator. A basic set of tools will usually suffice for most vehicles. Removing a door panel for the first time presents even the most experienced mechanic with challenges as it is easy to break the retaining clips or other components. When tackling this job it's advisable for amateurs and pros alike to consult a repair manual for door panel removal instructions. Care needs to be taken when disconnecting and reconnecting any linkages and wiring. Getting the part out of the door and installing the new one can be challenging because it is very confined and tight inside the door. Also, make sure to purchase the correct part before attempting replacement.