As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOTS REPORTED PRESSURIZATION FLUCTUATING, AND UNABLE TO CONTROL IN AUTO MODE. FILTERS ON CONTROLLER WERE CLEANED AND OUTFLOW VALVE WAS CLEANED. SYSTEM TESTED AS PER AIRCRAFT MAINTENANCE MANUAL AND OUTFLOW VALVE FOUND NOT TO BE OPENING. OUTFLOW VALVE CONTROLLER REPLACED AND WHEN TESTED OUTFLOW VALVE FOUND TO OPEN NORMAL. AIRCRAFT RETURNED TO SERVICE AND PRESSURIZATION REPORTED TO FUNCTION NORMAL.