FORD 2003 Expedition v.3 - Manual (Page 262)

When one of the rear wheels is off the ground, the transmission
alone will not prevent the vehicle from moving or slipping off the
jack, even if the transmission is in P (Park). To prevent the vehicle
from moving when you change the tire, be sure that the parking brake
is set and the diagonally opposite wheel is blocked. If the vehicle slips
off the jack, someone could be seriously injured.
• Front
• Rear
To lessen the risk of
personal injury, do not put
any part of your body under the
vehicle while changing a tire. Do
not start the engine when your
vehicle is on the jack. The jack is
only meant for changing the tire.
Roadside Emergencies
262