CITROËN C4 Handbook page 62

Access
Back-up control
System allowing the doors to be locked and
unlocked manually in the event of a malfunction
of the central locking system or battery failure.
Locking the driver's door
F Insert the key in the door lock, then turn it
to the rear.
You can also apply the procedure described for
the passenger doors.
Unlocking the driver's door
F Insert the key in the door lock, then turn it
to the front.
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Locking the passenger doors
F Open the doors.
F On the rear doors, check that the child lock
is not on.
For more information on the child lock, refer to
the corresponding section.
F Remove the black cap, located on the edge
of the door, using the key.
F Insert the key in the socket without forcing
it, then without turning it, move the latch
sideways towards the inside of the door.
F Remove the key and refit the cap.
F Close the doors and check that the vehicle
has locked correctly from the outside.
Unlocking the passenger doors
F Pull the interior door opening control.