As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT, RECEIVED "HYD PRES ENG 4" AND "HYD QTY LOW" MESSAGES. THE HYDRAULIC FLUID QUANTITY IN THE NBR 4 SYSTEM INDICATED ZERO. TURNED OFF THE HYDRAULIC PUMPS FOR THE NBR 4 SYSTEM AND THE CREW DECLARED AN EMERGENCY. ALTERNATE EXTENDED THE LANDING GEAR AND THE AIRCRAFT LANDED WITHOUT INCIDENT. REPLACED THE ENGINE DRIVEN HYDRAULIC PUMP. OPERATIONAL CHECK GOOD.