As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DURING FLIGHT THE CREW RECEIVED A STATUS MESSAGE FOR THE LEFT PACK FLOW CONTROL VALVE. THE DECESION WAS MADE TO RETURN TO FIELD. EMERGENCY WAS DECLARED, AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED UPPER LEFT FLOW CONTROL VALVE AMM 21-51-01.