What was found
ON APPROACH INTO PHX EN ROUTE FROM ATL RECEIVED ECAM MESSAGE FOR NOSE WHEEL STEERING FAULT, DECLARED EMERGENCY AND LANDED WITHOUT FURTHER EVENT. MAINTENANCE FOUND THE CENTRALIZED FAULT DISPLAY SYSTEM FAULTED BOTH BRAKE STEERING CONTROL UNIT CHANNELS FOR NLG SERVO CONTROL UNIT (6GC). DISCONNECTED AND RESET CONNECTOR AT NLG SERVO CONTROL UNIT (6GC), FAULT CLEARED AND DID NOT RETURN. REMOVED AND REPLACED NLG SERVO CONTROL UNIT (6GC) IAW AMM 32-51-51-04, LEAK AND OPERATIONAL CHECKS WERE GOOD. FUNCTIONAL TEST OF NLG SERVO CONTROL UNIT S/N U416 CONFIRMED REASON FOR REMOVAL, UNIT FAILED VOLTAGE BALANCE TEST, REPLACED SERVO VALVE PER CMM 32-57-01, REV. 8.