What was found
ON APPROACH TO SDL, A HYD VOLUME LOW CAS MESSAGE ANNUNCIATED WHEN THE GEAR WAS LOWERED. THE GEAR SUBSEQUENTLY LOCKED IN THE DOWN POSITION. HYDRAULIC PRESSURE SHOWED 3100 PSI WITH A VOLUME OF 110 CU IN. RAN QRH AND DIVERTED TO PHX DUE TO LOSS OF HYDRAULIC SYSTEMS; THE EMERGENCY BRAKE WAS USED TO STOP THE AIRCRAFT ON THE RUNWAY. NO HYDRAULIC LEAKS WERE SEEN WHEN A VISUAL INSPECTION WAS COMPLETED AFTER BEING TOWED TO THE RAMP. CORRECTIVE ACTION: REPLACED HYDRAULIC LINE IAW CE-680A SPM 20-10-75. OPS CHECK GOOD.