WARNING: This page is about a different car, the 2006 GMC Sierra and 2006 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View Of Engine Protection Shield
Courtesy of GENERAL MOTORS CORP.
Remove the frame to the shield bolts.
Remove the shield from the vehicle. 15 Series is shown, 25 Series is similar.