What was found
CABIN ALTITUDE HI CAS WARNING MESSAGE ILLUMINATED WHILE LEVELING AT 430. CABIN DID NOT SEEM TO GO ABOVE 10000FT AND PAX MASKS DID NOT DROP. ONCE AT 10000FT AIRCRAFT PRESSURIZATION DIFFERENTIAL SEEMED TO BE NOT NORMAL ALL THE WAY DOWN TO SEA LEVEL AND LANDING. TROUBLESHOT TO FAULTY PRESSURE RELIEF VALVE ( SEE STEPS FOR TROUBLESHOOTING.) REMOVED AND INSTALLED WITH A NEW PRESSURE RELIEF VALVE IAW AMM 21-31-04 . OPS CHECK AND LEAK CHECK GOOD. NO FURTHER DEFECTS NOTED.