All gasoline sold in the United States is required to contain effective detergent additives. Use of additional detergents or other additives is not needed under normal conditions and would result in additional cost. Therefore you should not have to add anything to the fuel.
See also:
Glow plug warming failure
The warning light on the dial flashing (on certain versions together with the
message on the display) when there is a failure in the glow plug warming system.
Contact Fiat Dealership as soon a ...
Engine
...
27. Fuel Gauge / Fuel Door Reminder
The fuel door reminder indicates that the fuel filler door is located on the
right side of the vehicle. When the ignition switch is in the ON/RUN position, the
digital scale will show the level of ...