As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING FROM 8000' TO 14000', YELLOW HYDRAULIC LOW PRESSURE INDICATION FOLLOWED BY LOSS OF YELLOW SYSTEM FLUID. FOLLOWED QRH PROCEDURES AND RETURNED TO BASE. PART NIS. ORDERED NEW POWER CONTROL UNIT FROM SFS CANNED FILTER ASSY FROM NEW POWER CONTROL UNIT AND INSTALLED SAME. RAN BOTH ENGINES PER A310 JRH. NO LEAKS NOTED.