Car won't start citroen c3 1.4 petrol

[Sick of car]

Hi can any help I brought citroen c3 vtr plus 1.4 petrol 61 plate 7 months ago I was driving it everyday no faults at all 3 weeks ago I was doing 50mph on duel carriageway and lost all power no warning rac give me fault code po122 and p2122 thunk it was had both replaced and reset and car still won't start keep saying low voltage we have checked battery starter motor spark plugs and coil pack fuel pump ok crankshaft sensor ok keep saying low voltage and won't start any help or idea's be much appreciated thanks

[mickthemaverick]

Low voltage errors can be due to a poor output from the alternator. You need to measure the voltage across the battery while cranking the engine on the starter, if it is too low (because the alternator is not kicking in to charge it when it is running) then the ecu will not fire it up.