How do you change serpentine belt on 2009 Buick lucerne?

To change the serpentine belt on a 2009 Buick Lucerne, first, ensure the engine is off and cool. Locate the serpentine belt tensioner and use a wrench or socket to relieve tension on the belt. Remove the old belt from the pulleys, then route the new belt according to the belt routing diagram usually found on a sticker under the hood. Finally, release the tensioner to secure the new belt in place and double-check its alignment.