Volume (VOL)
WARNING: This page is about a different car, the 2008 Isuzu Ascender, 2008 GMC Envoy, and 2008 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Rotate the volume knob in order to increase or decrease the volume. The left volume knob controls the left headphone and the right volume knob controls the right headphone.