Ford Focus 2004 Owner's Manual page 114

Driving
ULTRASONIC PARK DISTANCE
SENSOR
The system consists of ultrasonic
sensors in the rear bumper, one
controller and a speaker. The
system measures the distance to
the closest obstacle when reversing
and helps the driver to judge this
distance correctly by audible
signals.
112
The park distance sensor is
an auxiliary system which is
not intended to relieve the driver
of his responsibility for exercising
due care and attention. In
particular, some objects close to
the vehicle (approx. 30 cm) and
above or below the sensors may
not be detected by the park
distance sensor and cause
damage to the vehicle. Ultrasonic
waves, heavy rain and/or
conditions causing disruptive
reflections may lead to objects
not being detected by the
sensors. In addition, objects
which absorb ultrasonic waves
may not always be detected due
to their unfavourable surface
characteristics.
The system is activated
automatically after the ignition is
switched on and the reverse gear is
selected. A short tone will sound to
indicate system readiness.