As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAX - CREW RETURNED TO FIELD WHEN AFTER TAKEOFF THEY WERE UNABLE TO CONTROL PRESSURE IN EITHER AUTO OR MANUAL MODES. MAINTENANCE INSPECTED THE AIRCRAFT AND FOUND NO HISTORY IN THE MDC. MAINTENANCE PRESSURIZED THE AIRCRAFT TO APPROXIMATELY 4.5 PSI AND THERE WERE NO DISCREPANCIES NOTED. THE SYSTEM OPERATIONAL CHECK, AND OPERATIONAL CHECK FLIGHT, WAS GOOD. THE AIRCRAFT WAS RETURNED TO SERVICE. NO PARTS WERE REPLACED.