WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Drive Belt Routing 3.8L
Courtesy of GENERAL MOTORS CORP.
Lift or rotate the drive belt tensioner using a 15 mm box end wrench on the pulley nut.