As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LHR INFLIGHT T83/17DEC FRA TO ORD - LEFT HYDRAULIC QUANTITY INDICATION AND LOSS OF LEFT HYDRAULIC PUMP DURING CRUISE. DIVERTED TO LHR AND LANDED WITHOUT INCIDENT. REPLACED NUMBER ONE ENGINE PRIMARY HYDRAULIC PUMP. SYSTEM GROUND CHECKED NORMAL OPERATION.