Failure Indications
A malfunction of the Rear Park Assist sensors or system is indicated, during REVERSE gear engagement, by the instrument panel warning icon.

The warning icon is illuminated and a message is displayed on the multifunction display (if equipped). Refer to “Instrument Cluster Descriptions” in “Understanding Your Instrument Panel” for further information.
The sensors and wiring are tested continuously when the ignition is in the ON/RUN position. Failures are indicated immediately if they occur when the system is ON.
Even if the system is able to identify that a specific sensor is in failure condition, the instrument cluster display shall indicate that the Rear Park Assist system is unavailable, without reference to the sensor in failure condition.
If even a single sensor fails, the entire system must be disabled. The system is turned off automatically.
Test yourself
A quick Fiat 500 quiz: every answer comes with an explanation and a link to the manual page.