As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR RETURN DUE TO AFTER TAKEOFF CREW O2 DROPPED TO 10 PSI. RETURNED TO NORMAL AFTER LANDING. PLACARDED CREW 02 PRESS INDICATION ON EICAS PER MEL 35-11-02 SIT 1. PRESSURE TRANSDUCER INOPERATIVE. REPLACED TRANSDUCER AND RETURN TO SERVICE. (M)