I have a 2014 500L 0.9 engine and over the last couple of weeks it has started showing ‘start stop unavailable’ warning light and stalling at when idling at a junction or in traffic then struggling to restart. Last night it did it twice within a mile of leaving Home and I just managed to get it started and to limp home. Any thoughts? When trying to restart it sound a bit like flat battery with not enough umpf to start and when limping home last night felt like not enough power/fuel getting to engine, couldn’t run above 2nd gear. Only had it 3 months and otherwise been thrilled with it ?

1st call is to check battery terminals for cleanliness and tightness
2nd call is to check the ground strap(s) from battery negative to chassis to engine
3nd call is to get the battery checked and/or replaced.

All modern cars (including Fiats) are very fussy about good battery and electrical connections and once these are not 100% OK then things start to play up big time.