We report these 2 cases resolved on FIAT 500X, specifically 1.6 and 2.0 mjet: in the morning at first start-up the cars activate the MIL light Engine Failure + start stop not available with error in memory P0115 Engine Temperature - Plausibility

The problem is not due to the engine temperature sensor or thermostat, but rather to the external temperature sensor integrated in the RIGHT rear-view mirror, in fact on both cars the external temperature reported was 99 C°, the engine control unit most likely performs a comparison between the engine temperature and the external temperature at cold start, setting error P0115.

Since the temperature sensor cannot be supplied individually, but rather in the rear-view mirror assembly, it has been fitted as a spare, or alternatively 10 kOhm universal temperature probes can be fitted.

I hope it can be useful to someone.
Greetings