What was found
AIRCRAFT WAS GROUNDED: YELLOW HYDRAULIC SYSTEM RESERVOIR LOW LEVEL MESSAGE CAME ON AFTER TAKEOFF. RESERVOIR INDICATES 0 FLUID. GEAR AND FLAPS WERE ALREADY FULLY RETRACTED. APPROXIMATELY 30 MINUTES LATER YELLOW HYDRAULIC SYSTEM RESERVOIR OVERHEAT MESSAGE CAME ON WITH THE YELLOW ELECTRIC PUMP OFF. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT LANDED SAFELY AT DFW. **ORIGINAL REPORT WAS AALA202206237990**: MAINTENANCE FOUND #2 PYLON ENGINE HYDRAULIC PRESSURE LINE LEAKING DUE TO A CRACK AND REPLACED IT. MAINTENANCE ALSO REPLACED THE #2 ENGINE DRIVEN HYDRAULIC PUMP DUE TO FAILURE. (AALA202206247428) A SATISFACTORY LEAK / OPERATIONAL CHECK WAS ACCOMPLISHED.