As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WOULD NOT PRESSURIZE ON ONE PACK, OUTFLOW VALVE SHOWED CLOSED. *S/D* REPLACED LEFT HAND ENGINE HIGH STAGE VALVE PER MM, HIGH STAGE VALVE FOUND INOP. RAN ENGINES AND PRESSURIZED AIRCRAFT, AIRCRAFT PRESSURE CONTROL SYSTEM CHECKED NORMAL.