Transfer Case
WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Remove fill plug. Check oil level. If oil level is even with bottom of fill plug opening, level is okay. If level is lower than bottom of fill plug opening, add lubricant as necessary.