As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE CREW REPORTED THAT AFTER TAKEOFF THE CABIN ALTITUDE WOULD CLIMB UNTIL A ALTITUDE OF 4000 FT WAS REACHED AND THEN THE CABIN ALTITUDE WOULD STAY AT 4000 FT DURING CLIMB AND CRUISE. IT WAS NOTED THAT THE CABIN WOULD DESCEND NORMALLY TO THE SELECTED FIELD ELEVATION. TROUBLESHOT AND FOUND THAT THE PRIMARY OUTFLOW VALVE DEFECTIVE. R & R THE OUTFLOW VALVE PN 9912409-7, SN 548 INSTALLED A MODIFIED PRIMARY OUTFLOW VALVE. FUNCTIONAL CHECKS SATISFACTORY.