CITROËN DS 5 Handbook page 258

In the event of a fault with the ScR emissions control system
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 self-diagnosis of the SCR 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 display of a message
(e.g.: "Emissions fault: Starting prevented in
150 miles") indicating the remaining range
express in miles or kilometres.
While driving, the message is displayed 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.