What was found
CPDLC WORKS FOR DCL BUT WILL NOT STAY LOGGED ONTO KUSA ENROUTE, FOLLOWED FLIGHT OPERATIONS BULLETIN RESET PROCEDURE WITHOUT SUCCESS. GROUNDED - YES. OMF SHOWS FAULT NSG 23-23011 NOT ACTIVE ON PRESENT LEG, PERFORMED SUCCESSFUL TEST NO DISCREPANCIES PER B737-9 IFIM 23-70-00-810-820, DUE TO FAULT MSG 23-23011 IN THE PAST HISTORY, REPLACED NEW SDU FOR PRECAUTION, R& R SDU & PERFORMED GOOD INSTALLATION TEST B737-9 AMM 23-15-01/401, REMOVED SDU PLACED SOS.