As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOTH FMC/ CDU UNITS REQUIRE MULTIPLE PUSHED OF SAME BUTTONS TO COMMUNICATE USING CPDLC. EX. USING LINE SELECT KEYS TO REPORT BACK ON COURSE ENROUTE REQUIRED MULTIPLE PUSHES TO WORK. GROUNDED - YES. PERFORMED CPDLC FUNCTIONAL TEST PER B737-800 AMM 33 34-61-00-720-899- ALL TESTS PASS. PERFORMED TEST OF LEFT AND RIGHT MCDU KEYPADS PER B737-800 FIM 34-61 TASK 801- ALL TESTS PASS.