As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED. DECLARED AN EMERGENCY LANDING AT SFO ACCOUNT OF A YELLOW HYDRAULIC SYSTEM PROBLEM. FLIGHT LANDED WITHOUT INCIDENT. AIRCRAFT WAS TOWED TO THE GATE. MAINTENANCE FOUND YELLOW HYDRAULIC SYSTEM RESERVOIR INDICATES EMPTY, DRAIN VALVES AND SEALS ON YELLOW HYDRAULIC SYSTEM NEED TO BE REPLACED. REPLACED DRAIN VALVE PER PER MM 29-13-41. ACCOMPLISHED SATISFACTORY OPERATIONAL CHECK.