CITROEN DS5 Owner's Handbook Manual page 142

The foglamps operate with dipped and main beam headlamps.
Front and rear foglamps
Rotate and release the ring:
forwards a first time to switch on the front
foglamps,
forwards a second time to switch on the
rear foglamps,
rearwards a first time to switch off the rear
foglamps,
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.
Turn the ring rearwards to switch off the
foglamps, the sidelamps will then switch
off.
In good or rainy weather, 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 snow.
In these weather conditions, it is your
responsibility to switch on the foglamps
and dipped headlamps manually as the
sunshine sensor may detect sufficient
light.
Do not forget to switch off the front
foglamps and the rear foglamps when
they are no longer needed.