How can I fix my window switch that has stopped working properly?

You can try using contact clener spray in to the switch after you take it off your door and if it still does not work then you can order from the internet and change it by yourself. Is not a difficult task to do.

I researched this question pretty carefully. Here's what I learned:

• The problem is extremely common in BMW 3 series cars (esp. 325 and 325xi). It is especially common with rear windows on 4-door sedans.
• It is caused, most of the time, by a part called a "window regulator." There is one inside each door, and most of the time, it has to be replaced.
• The part itself is not so expensive, but because the door has to be taken apart, the labor cost is high. I had to get this done here in Philly, mainly because I know the limits of my competence and I'm not quite ready to risk wrecking my own car while trying to fix it. All in all, it cost over $300 - and that was for one window.
• Incidentally, the problem is most common in BMW 3 series cars, 2001-2006, with average mileage of 101,745 miles (range is 9,000 to 280,000 mi.).

I downloaded and have attached a diagnostic chart that can help you determine whether the window regulator needs to be replaced. Hope it's helpful.

windowregulatorflowchart.pdf

The answerto your question although it's useless 9 years later but very usefull for people like me is - the rubber on the inside that clicks the button.When you remove the shift leather and the plastic you will see the module ,open it and you will find 6 clips open them from the bottom try to push the part inside down.Then you will see the mechanism and you will notice a fault in the rubber making the contact for your command,it's broken.Now switch them so you can use the front window which is more usefull.