The passenger seat has a pressure switch mounted on the bottom.
It is designed to turn off the passenger side front airbag if there is someone smaller than an "adult" occupying the seat.
If it comes on when no one and nothing is in the seat, the dealer will need to calibrate it.
This is from the 2010 owners manual. But all years are similar 08-11.
"The Occupant Classification System (OCS) is part of
a Federally regulated safety system required for this
vehicle. It is designed to turn off the front passenger
airbag for an empty seat and for occupants classified
in a category other than that of an adult. This could be
a child, teenager, or even a small size adult."
"The Passenger Airbag Disable (PAD) Indicator Light
(an amber light located in the center of the instrument
panel) tells the driver and front passenger when the
front passenger airbag is turned off. The “PAD Indicator
Light” illuminates the words "PASS AIR BAG
OFF" to show that the passenger airbag will not inflate
during a collision requiring airbags. When the front
passenger seat is empty or when very light objects are
placed on the seat, the passenger airbag will not inflate
even though the “PAD Indicator Light” is not illuminated."
Since the system senses weight, some small objects
will turn the PAD Indicator Light on.
If you are interested you can down load a search-able owners manual
Here.