As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - CREW REPORTED CENTER INERTIAL REFERENCE UNIT FAILED WITH RIGHT IRU ON PLACARD. EMERGENCY DECLARED FLIGHT RETURNED ORD LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED CENTER INERTIAL REFERENCE UNIT. SYSTEM GROUND CHECK NORMAL OPERATION.