What was found
FLT 625 - PHX-OAK - RTF - CREW REPORTED TOTAL LOSS OF YELLOW SYSTEM HYDRAULIC FLUID. DESELECTED PTU AND ENG NR 2 YELLOW PUMP PER ECAM, HOWEVER BOTH RAN WITHOUT FLUID FOR SHORT PERIOD. ELECTRIC YELLOW PUMP WAS NOT ACTIVATED. CREW DECLARED AN EMERGENCY AND RETURNED TO PHX. MAINTENANCE REMOVED AND REPLACED THE POWER TRANSFER UNIT. ALSO REMOVED AND REPLACED THE YELLOW SYSTEM NR 2 ENGINE DRIVEN PUMP FOR PRECAUTIONARY MAINTENANCE. OPERATIONAL CHECK GOOD. HYDRAULIC PUMP ASSEMBLY / MFGR EATON / MFG P/N 887673 / MFG S/N MX607895 / PART CONDITION UNKN / PART LOCATION ZONE 400 NACELLES/PYLONS / TOTAL TIME 28608 / TOTAL CYCLES 11272 / TIME SINCE REPAIR 1462.