CITROEN DS3 Owner's Handbook Manual page 172

Stop & Start
The Stop & Start system puts the engine temporarily into standby - STOP mode - during stops in the traffic (red lights, traffic jams, etc...). The engine
restarts automatically - START mode - as soon as you want to move off. The restart takes place instantly, quickly and silently.
Perfect for urban use, the Stop & Start system reduces fuel consumption and exhaust emissions as well as offering the comfort of silence when
stationary.
Operation
Going into engine STOP mode
The "ECO" warning lamp comes
on in the instrument panel and the
engine goes into standby:
- with a manual gearbox , at speeds below
12 mph (20 km/h), when you put the gear
lever into neutral, and you release the
clutch pedal,
A time counter calculates the sum
of the periods in STOP mode
during a journey. It rests itself
to zero every time the ignition is
switched on with the key.
For your comfort when parking, STOP
mode is not available for a few seconds
after coming out of reverse gear.
STOP mode does not affect the
functionality of the vehicle, such as
braking, power steering, for example.
Never refuel with the engine in STOP
mode; you must switch off the ignition
with the key.
Special cases: STOP mode
unavailable
STOP mode is not invoked when:
- the driver's door is open,
- the driver's seat belt is not fastened,
- the vehicle has not exceeded 6 mph
(10 km/h) since the last engine start using
the key,
- the engine is needed to maintain a
comfortable temperature in the passenger
compartment,
- demisting is active,
- some special conditions (battery charge,
engine temperature, braking assistance,
ambient temperature...) where the engine is
needed to assure control of a system.
The "ECO" warning lamp flashes for
a few seconds, then goes off.
This operation is perfectly normal.