As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED THAT DURING FLIGHT, THE AIRCRAFT WOULD NOT PRESSURIZE IN AUTOMATIC OR MANUAL MODES. THE CREW RETURNED TO FIELD AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE EXTERNAL GROUND CONNECTION VALVE COVER TO BE MISSING AND DEFERRED THE ITEM. THE DEFERRAL WAS CLEARED ON 1/10/2013 WHEN THE EXTERNAL GROUND CONNECTION VALVE COVER WAS REPLACED. OPERATIONAL CHECKS OF THE PRESSURIZATION WERE GOOD WITH NO FURTHER DEFECTS NOTED.