Take your door panel off and replace them...
The way that replace a window regulator in a 2003 Buick LeSabre front drive side is by removing the door panel. Next, disconnect the electrical connector on the regulator and replace.
Yes
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Most likely it is the regulator, either the cable is broken or the plastic at the top broke and the cable became unspooled and wrapped around itself. The window is held in by two screws that tighten a clamp on the window that holds pretty tight so it is doubtful it is that.
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See this post for instructions and photoshttp://www.ricksfreeautorepairadvice.com/repair-topics/window-power-repair/replace-a-power-window-regulator
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To put the power window of a 2003 Buick Rendezvous back on track, first, remove the door panel to access the window mechanism. Ensure that the window is in the fully closed position, then carefully realign it within the track by pushing it back into place. Check the window regulator and ensure that any clips or guides are securely attached. Finally, test the window's operation before reassembling the door panel.