Originally Posted by 70GT6
more owners manual:
The central locking switch also operates the automatic
central locking feature. With the automatic central locking
feature activated, the doors and rear liftgate/decklid
are locked at vehicle speeds of approximately 9 mph (15
km/h) or more; however, the fuel filler door remains
unlocked.
Just in case you want to do something like a "mid air refueling".
Keep your airspeed up!