A320 FLT CREW HAS A FAILURE OF THEIR NAVIGATIONAL INSTS DURING AN APCH TO ORD.

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WE WERE ON A VECTOR TO INTERCEPT THE RWY 9R ILS AT ORD. THE ACFT WAS CONFIGURED TO FLAPS 2 DEGS; ASSIGNED AIRSPD 180 KTS (MINIMUMS) AT 2500 FT MSL. ORD APCH GAVE US AN INTERCEPT HEADING TO THE LOC AND DIRECTED US TO INTERCEPT IT. THE PF ARMED THE LOC BUTTON. BOTH PLTS NOTED THE LOC ON THE FLT MGMNT ANNUNCIATOR (FMA). UPON RECEIVING APCH CLRNC; THE FO DEPRESSED THE APCH BUTTON AND SELECTED THE SECOND AUTOPLT. THE BUTTON DID NOT ILLUMINATE GREEN; NOR WERE THERE BLUE ARMED INDICATIONS ON THE FMA. THE FO'S AUTOPLT SWITCHED TO THE CAPT. AT THE SAME TIME THE CAPT'S #2 FLT DIRECTOR WAS DIRECTING A COURSE INTERCEPT WHILE THE FO'S FLT DIRECTOR NEEDLES WERE SWINGING STOP TO STOP AND HIS RAW DATA WAS ALSO FLUCTUATING. AS WE WERE IMC; THE CAPT ORDERED A GAR. RPTING THIS TO APCH; HE SENT US TO TWR. TWR PROVIDED VECTORS AND SENT US BACK TO APCH. ON EXTENDED DOWNWIND; WE EVALUATED OUR EQUIP AND ELECTED TO FLY THE LOC RWY 9R (NO GS). OPS WERE NORMAL; SO WE SELECTED APCH. ITS OP WAS NORMAL AS WELL AS THE LNDG AND ROLLOUT. EXITING THE RWY THE ECAM (ELECTRONIC CENTRALIZE ACFT MONITOR) DISPLAYED A CLASS I; LEVEL 3 FAULT: AUTOFLT FCU (FLT CTL UNIT) #1 FAULT. IN 30 SOME YRS OF FLYING; IT WAS THE FIRST TIME I HAVE OBSERVED THIS SORT OF THING. YOU THINK ABOUT IT; PLAN FOR IT; NEVER EXPECTING IT TO HAPPEN TO YOU.