What was found
CMH - DIVERSION - FLT 0249 - EN ROUTE FROM PHX TO PHL, DURING CRUISE AIRCRAFT EXPERIENCED AN ECAM MESSAGE FOR YELLOW SYSTEM HYDRAULIC LOW PRESSURE. CHECKED QTY, INDICATED EMPTY. INFLIGHT DIVERTED TO CMH ECAM ACTIONS COMPLETED. REMOVED AND REPLACED O-RING AT NR 2 ENGINE PRESSURE TRANSDUCER. SERVICED YELLOW SYSTEM, LEAK CHECK PERFORMED, NO LEAKS NOTED.