As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN ENROUTE, THE AIRCRAFT CABIN PRESSURIZATION WARNING LIGHT AND HORN CAME ON. THE FLIGHT CREW RETURNED, WITHOUT FURTHER INCIDENT. MAINTENANCE INSPECTED THE PRESSURIZATION SYSTEM AND FOUND THE PRESSURIZATION CONTROLLER TO BE MALFUNCTIONING AND REPLACED THE DEFECTIVE CONTROLLER. (K)