As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: AUTO PRESSURIZATION FAIL LIGHT CAME ON DURING CLIMBING THROUGH FL340. AIRCRAFT DIVERTED TO AND LANDED SAFELY AT ORD. REMOVED AND REPLACED AFT OUTFLOW VALVE ASSEMBLY. PER AMM 21-31-03.