As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AIRCRAFT RETURNED TO LAX DUE TO A PACK 1 FAULT MESSAGE. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT LANDED SAFELY AT LAX WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE PACK 1 FLOW CONTROL VALVE 11HB PER AMM 21-51-51. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.