As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNABLE SAT COMMUNICATION. TRIED MULTIPLE TIMES TO TRANSMIT AND RECEIVE SATCOM ON CAPTAIN'S SIDE AND FIRST OFFICER'S COMM PANEL ON SAT 1 AND SAT 2. DISPATCH COULD HEAR OUR TRANSMISSION WHILE DISPATCH COULDN'T RECEIVE (HEAR) OUR TRANSMISSION. GROUNDED - YES. ACCOMPLISHED B737-800 AMM 23-15-00-730-801 "SATCOM COMMUNICATION SYSTEM TEST", CONTACTED DISPATCH, OPS CK NORMAL.