CITROËN 2014 C4 Picasso Handbook page 328

Checks
F Without pressing, turn the black cap a
quarter turn anti-clockwise and lift it off.
326
F Turn the blue cap a 6
th
of a turn anti-
clockwise.
F Lift off the cap.
F Obtain a bottle of AdBlue . After first
®
checking the use-by date, read carefully
the instructions on use on the label before
pouring the contents of the bottle into your
vehicle's AdBlue tank.
®
Important: if your vehicle's
AdBlue tank is completely empty -
®
which is confirmed by the alert
messages and the impossibility of
starting the engine, you must add at
least 3.8 litres (so two 1.89 litre bottles).