What was found
ON TAKEOFF ROLL AT PHX EN ROUTE FOR OAK TAKEOFF WARNING CONGIURATION HORN SOUNDED, REJECTED TAKEOFF AT 55 KTS. AFTER CLEARING THE RUNWAY CHECKED SETTINGS, ALL WERE NORMAL, CYCLED FLAPS AND RAN UP TO POWER, NO HORN. SUBSEQUENT TAKEOFF WAS NORMAL. A FOLLOW UP WAS WRITTEN TO PERFORM A TAKEOFF WARNING SYSTEM TEST, WHEN AIRCRAFT ARRIVED BACK IN PHX TAKEOFF WARNING SYSTEM TEST WAS C/W IAW T/C A1B31009, TEST PASSED WITH NO DEFECTS NOTED.