corsa 1.2 semiauto 2003 flashing " f "

HI TO ALL I JUST BUY CORSA 1.2 SEMIAUTO 2003 WITH 70000 MILES CAR WAS START AND DRIVE PERFECT TILL DAY BEFORE XMASS IM MORNING CANT START THE CAR I CALL MECHANIC HE REPLACE CRANK SENSOR FINALY CAR STARTS NEXT DAY SAME PROBLEM CANT START CAR AND " F " START FLASHING ON DASH ANY ONE HAVE...