The power windows of your BMW are probably among the greatest conveniences your vehicle is equipped with. Imagine, you won't have to bother winding down the windows manually each time you have to pay on the toll booth or take your orders from a drive-thru restaurant. You won't even have to exert much effort to lower the windows whenever you have to explain something to the traffic officer (guilty?). All you have to do is press a button and instantly, the window glasses would go up or down. You see? Everything seems so convenient with the power windows... until something goes wrong.
A BMW power window unit is basically composed of four parts (minus all the electrical wirings that connects one electronic component to another). These parts include the BMW window motor, window regulator, window switch and window relay. The BMW window motor is the small electric motor, usually installed beneath the vehicle doors, which powers the window regulator. The window regulator, on the other hand, is the mechanical assembly that opens and closes the glass windows depending on the direction of the motor's rotation. You control the BMW power window through the window switch, which in turn is connected to the vehicle's battery or to some electronic module by the window relay.
Now, whenever the power windows of your BMW won't work properly, any of these four components can be the culprit. If the windows won't wind up or down whenever you press the power window switch and you don't hear any apparent activity in the motor, then the problem is probably on the window switch or on the window relay. It may be caused by a damaged electrical wiring or damages on the relay or the switch itself. Alternatively, this may also mean that the window motor has totally died, although this situation is kind of rare unless the motor had previous problems that were not given attention.
But if the problem is manifested by a slowly winding window glass, then problems in the window switches and window relays should be ruled out. In such cases, the problem would belong to either the window motor or the window switch. One possible scenario is that the regulator is already weak and beginning to fail. Another is that a part of the regulator is already broken. But if the window glass is moving intermittently each time it is winded up or down, the problem is probably a shorted or deteriorating window motor.
So if the power windows of your BMW are already malfunctioning, better determine immediately which parts have problems and replace or repair them immediately. Here at Parts Train, we have a large inventory of BMW window motors and window regulators that you can make use of in case those are causing the problem. Depending on your BMW's model, we also have BMW window regulators and motors that are sold as a single unit.