As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING CRUISE FLIGHT AT FL270, THE CREW EXPERIENCED A CABIN HI ALT LIGHT. BLEED FLOW WAS INCREASED AND THE CABIN ALT DESCENDED, EXTINGUISHING THE LIGHT. MAINTENANCE INVESTIGATION REVEALED THAT THE AFT OUTFLOW VALVE WAS NOT CLOSING COMPLETELY. THE CABIN PRESSURIZATION CONTROLLER WAS REPLACED AND THE OUTFLOW VALVE OPERATED NORMALLY. THE CONTROLLER HAD BEEN REPAIRED 1059 HOURS AND 677 CYCLES PREVIOUS.