GMC Yukon Owner's Manual page 90

3. Be sure that the belt is not twisted and it lies flat.
The elastic cord must be under the belt and the
guide on top.
2-52
WARNING:
A safety belt that is not properly worn may
not provide the protection needed in a crash.
The person wearing the belt could be seriously
injured. The shoulder belt should go over the
shoulder and across the chest. These parts of the
body are best able to take belt restraining forces.