CITROEN DS5 Owner's Handbook Manual page 136

Front parking sensors
In addition to the rear parking sensors, the front
parking sensors are triggered when an obstacle
is detected in front and the speed of the vehicle
is still below 6 mph (10 km/h).
The front parking sensors are interrupted if
the vehicle stops for more than three seconds
in forward gear, if no further obstacles are
detected or when the speed of the vehicle
exceeds 6 mph (10 km/h).
The sound emitted by the speaker (front
or rear) indicates whether the obstacle
is in front or behind.
Deactivation / Activation of the
front and rear parking sensors
The function is deactivated by pressing this button.
The indicator lamp in the button comes on.
Pressing this button again reactivates the function.
The indicator lamp in the button goes off.
The function will be deactivated
automatically if a trailer is being towed
or a bicycle carrier is fitted (vehicle
fitted with a towbar or bicycle carrier
recommended by CITROËN).
Operating fault
In the event of a malfunction
of the system, when reverse
gear is engaged this warning
lamp is displayed in the instrument panel
and/or a message appears in the screen,
accompanied by an audible signal (short beep).
Contact a CITROËN dealer or a qualified
workshop.
In bad weather or in winter, ensure
that the sensors are not covered with
mud, ice or snow. When reverse gear is
engaged, an audible signal (long beep)
indicates that the sensors may be dirty.
Certain sound sources (motorcycle,
lorry, pneumatic drill, etc.) may trigger
the audible signals of the parking
sensor system.