As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: VENT AVIONICS SYSTEM FAULT ON ECAM. CREW FOLLOWED ECAM ACTIONS AND AIRCRAFT WOULD NOT PRESSURIZE SUFFICIENTLY. (ORIGINAL ECAM WAS VENT SKIN VALVE FAULT). AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO SFO WHERE IT LANDED SAFELY WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED SKIN AIR OUTLET VALVE PER AMM 21-26-53-00-002-A AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 21-26-00.