As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DIVERTED TO ORD DUE TO A COCKPIT OXYGEN PRESSURE PROBLEM. THE PROBLEM COULD BE ATTRIBUTED TO A FAULTY O2 SYS SERVICING FILLER VALVE. REPLACED CREW O2 SYS SERVICING FILLER VALVE. REPLACED CAPTAIN'S AND OBSERVER'S O2 MASKS.ALSO REPLACED FIRST OFFICERS O2 STORAGE BOX. ALL 3 CREW OXYGEN MASK HOLDERS REMOVED AND OXYGEN LINES CAPPED.