As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
COULD NOT PRESSURIZE AIRCRAFT ON CLIMBOUT. DOWNLINKED CMC DATABASE SHOWED MAINTENANCE MESSAGE 21-39080, THE CABIN PRESSURE COULD NOT BE CONTROLLED DUE TO FAILED AFT OUTFLOW VALVE CONTROL UNIT (VCU). AFTER REPLACING THE FAILED ACTUATOR ASSY (COMPRISED OF THE VCU) WITH A SERVICEABLE ONE, THE AIRCRAFT RETURNED TO SERVICE.