CITROËN DS 5 Handbook page 146

Foglamp selection ring
The foglamps operate with dipped and main beam headlamps.
Front and rear
foglamps
Rotate and release the ring:
F forwards a first time to switch on the front
foglamps,
F forwards a second time to switch on the
rear foglamps,
F rearwards a first time to switch off the rear
foglamps,
F rearwards a second time to switch of the
front fog lamps.
When the headlamps switch off with automatic
illumination of headlamps (AUTO model)
or when the dipped beam headlamps are
switched off manually, the foglamps and
sidelamps remain on.
F Turn the ring rearwards to switch off
the foglamps, the sidelamps will then
switch off.
In good or rainy weather, by both day
and night, the front foglamps and the
rear foglamps are prohibited. In these
situations, the power of their beams
may dazzle other drivers. They should
only be used in fog or falling snow.
In these weather conditions, you should
switch on the foglamps and dipped
beam headlamps manually, as the
sunshine sensor may detect sufficient
light.
Do not forget to switch off the front and
rear foglamps when they are no longer
necessary.