CITROEN DS4 Owner's Handbook Manual page 220

To deactivate the system, press this button
again; the warning lamp goes off.
The state of the system remains in memory on
switching off the ignition.
The system is automatically
deactivated when towing with a towbar
approved by CITROËN.
Operating fault
In the event of a fault, the warning lamp in the
button flashes then goes off.
Have it checked by a CITROËN dealer or a
qualified workshop.
The system may suffer temporary
interference in certain weather
conditions(rain, hail...).
In particular, driving on a wet surface
or moving from a dry area to a wet area
can cause false alerts (for example, the
presence of a fog of water droplets in
the blind spot angle is interpreted as a
vehicle).
In bad or wintry weather, ensure that
the sensors are not covered by mud,
ice or snow.
Take care not to cover the warning
zone in the door mirrors or the
detection zones on the front and rear
bumpers with adhesive labels or other
objects; they may hamper the correct
operation of the system.