As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AS THE AIRCRAFT WAS TAXING OUT FOR DEPARTURE THE RT HYDRAULIC SYSTEM LOST FLUID AND PRESSURE. THE AC RETURNED TO THE GATE WITHOUT ANY FURTHER PROBLEMS. MAINTENANCE FOUND THE RT HYDRAULIC SYSTEM PRESSURE RELIEF VALVE HAD FAILED AND REPLACED IT. ALSO THE RT ELECTRIC HYDRAULIC PUMP WAS REPLACED AS A PRECAUTION. LEAK CHECK AND OPERATIONAL CHECKS WERE GOOD AND THE AIRCRAFT WAS RETURNED TO SERVICE.