I had the same problem and fixed it myself. You have to remove the door panel and plastic cover behind it. You will see that the window rides up and down on two vertical tracks supported by a horizontal rail .The rear trackl has a plastic roller/wheel that rides in it. On my car the shaft that is pressed into the wheel popped out so that the wheel was in the vertical track but the window was not supported in the rear. This is caused by pulling and pushing on the top of the window when getting in and out of the car. Remove the bolts on the vertical track and work it out of its position so you can get the wheel out of the track from the top . Press the wheel back on the shaft with a very large pair of plyers. It will seem like it doesn't fit, but squeeze and it will pop on. Then slide the track back on and bolt it up. Don't let people push on the window when they close the door.