Turning the key to MAR the warning light on the dial turns on, but it should go off as soon as the engine is started.
If the 
warning light turns on when
the car is travelling (on certain versions together with the message on the display),
stop the engine immediately and contact a Fiat Dealership.
See also:
Cleaning The Rear Park Assist System
Clean the Rear Park Assist sensors with water, car wash soap and a soft cloth.
Do not use rough or hard cloths. In washing stations, clean sensors quickly keeping
the vapor jet/high pressure washi ...
Capacities
(❒) For use with very cold temperatures we recommend using SELENIA PERFORMER
MULTIPOWER SAE 5W-30.
...