Cadillac 2004 CTS Owner's Manual page 30

3. To make the lap belt part tight, pull down on the
buckle end of the belt as you pull up on the
shoulder part.
1-24
The lap part of the belt should be worn low and snug on
the hips, just touching the thighs. In a crash, this applies
force to the strong pelvic bones. And you'd be less likely
to slide under the lap belt. If you slid under it, the belt
would apply force at your abdomen. This could cause
serious or even fatal injuries. 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.