Buick Regal Owner's Manual page 54

2-20 Keys, Doors, and Windows
Sunshade
The sunshade is manually operated.
Close or open the sunshade by
sliding. When the sunroof is
opened, the sunshade is
always open.
Safety Function
If the sunroof has any resistance
during automatic closing, it will
immediately stop and reverse.
To override the safety function,
press and hold the close sunroof
switch. The sunroof closes without
the safety function. To stop the
movement, release the switch.