1991 Mercedes-Benz 300E Window Regulator Motor Replacement Cost

The electric window motor on older cars featured an electrical circuit that was activated by pressing the window switch in the passenger compartment. When the switch was pressed, an electrical circuit would close and operate the motor. Modern vehicles employ an electronic signal originating from an onboard computer (electronic control unit, or ECU) to trigger the window motor. In addition to being actuated by the window switch, newer systems also allow the window to be controlled by a signal from the key fob.

If the door window motor fails, the window may not open or close, or it may operate intermittently. Traditionally, problems with power windows were caused by faulty switches or electrical wiring - especially the wires running between the door and the vehicle body that are subjected to repeated flexing. In these cases, the window might operate intermittently when the door is opened and closed. While this may still be the case on newer cars, it is increasingly common to find window motor problems that originate with a control module. Still, the switches and wiring should be checked thoroughly before replacing a window motor.

It is possible to drive a vehicle with a faulty window motor, depending on weather conditions, since the window may be stuck in the down position. Your vehicle may also be vulnerable to theft if the window is left down.

Window motors are generally reliable and do not need to be replaced very often. If a window motor is integrated into a window regulator that fails, then the motor and regulator will need to be replaced together.

A technician will being diagnosis of a faulty window motor by actuating the switch and listening for sound from the motor. If there is no sound, a technician will first check the relevant fuse. Next, a technician might observe the interior dome light while operating the switch. If the dome light dims, the motor is likely to be broken. For final verification of a bad motor, the door trim panel will need to be removed so that the wiring harness connector to the motor can be checked for voltage. A technician may even be able to use a professional diagnostic scan tool to locate a potential problem with the vehicle's wiring in a late model vehicle.

Replacement of a window motor depends on the type of vehicle and style of window regulator. Generally, 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 or motor are not functioning properly) and either held in place or removed from the door. Finally, the regulator is removed from the door and the faulty motor is exchanged for a new one. If the motor is integrated into the window regulator, the entire assembly will have to be replaced.

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. On some vehicles, the window regulator may have to be replaced with the window motor. A manual can also give important information for resetting the control module on some vehicles.

When replacing a window motor 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 window motor 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. Additionally, some vehicles require a computer reset after a window motor or switch has been installed. Consult a repair manual for specifics.