GMC 2005 Safari Owner's Manual page 82

Canceling the Sliding Door
Security Lock
To cancel the security lock, do the following:
1. Unlock the door and open it from the outside.
2. Move the lever all the way down.
2-10
CAUTION:
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If your vehicle is facing downward on a steep
grade (15 percent or more), the door may not
stay open and could slam shut, possibly
injuring someone. To make sure the door does
not slam shut be sure to hold it open until
everyone is clear of the door, and only then
allow it to slowly close.