CITROEN Grand C4 PICASSO Owner's Handbook Manual page 316

Checks
The petrol or Diesel engine of your vehicle is
fitted with a catalytic converter, a device which
helps to reduce the level of harmful emissions
in the exhaust gases.
For petrol engines, you must use unleaded
fuel.
The filler neck is narrower, allowing only
unleaded petrol nozzles to be introduced.
If you have put in the wrong fuel
for your vehicle, you must have the
fuel tank drained and filled with
the correct fuel before starting the
engine.
314
Fuel cut-off
Your vehicle is equipped with a safety device
which cuts off the fuel supply in the event of a
collision.