CITROËN DS 4 Handbook page 300

In the event of a fault with the the SCR emissions control system
Type 1 instrument panel
A system that prevents engine starting is activated automatically from 650 miles (1 100 km) after confirmation of a fault with the SCR emissions
control system. Have the system checked by a CITROËN dealer or a qualified workshop as soon as possible.
In the event of the detection of a fault
The UREA, SERVICE and diagnostic warning
lamps comes on, accompanied by an audible
signal and the display of the message
"Emissions fault".
The alert is triggered when driving, when
the fault is detected for the first time, then
when switching on the ignition for subsequent
journeys, while the fault persists.
If it is a temporary fault, the alert
disappears during the next journey,
after a self diagnosis test of the SCR
emissions control system.
during an authorised driving phase
(between 650 miles and 0 miles) (1 100 km and 0 km)
If a fault with the SCR system is confirmed (after
30 miles (50 km) covered with the permanent
display of the message signalling a fault), the
SERVICE and engine diagnostic warning lamps
come on and the UREA warning lamp flashes,
accompanied by an audible signal and the
temporary display in the instrument panel of
"NO START IN" and a distance, indicating the
remaining range express in miles or kilometres
before engine starting is prevented - (e.g.:
"NO START IN 350 miles" means "Starting will
be prevented in 350 miles").
While driving, this display appears every
30 seconds while the fault with the SCR system
persists.
The alert is repeated when switching on the
ignition.
You should go to a CITROËN dealer or a
qualified workshop as soon as possible.
Otherwise, you will not be able to restart your
engine.