Pioneer AVIC-505 Owner's Manual page 131

When is it used?
GPS is used to determine your position whenever adequate signals are available. However,
there are times when this is not possible and the system has to rely on an estimated position (see
"Dead reckoning" below).
• If signals can be picked up from no more than two GPS satellites, GPS positioning does not
take place.
• Under some driving conditions, signals from GPS satellites may not reach your vehicle. In
this case, it is not possible for the system to use GPS positioning.
In tunnels or enclosed
parking garages
When driving among
high buildings
• GPS reception may be lost temporarily if a car phone or cellular phone is used near the GPS
aerial.
Care of the GPS aerial
Do not obstruct the GPS aerial with spray paint or car wax, as this may block the reception of
GPS signals. Snow buildup may also degrade the signals, so keep the aerial clear.
Under elevated roads or
similar
When driving trough
dense forest or tall trees