As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: LAVATORY SMOKE EICAS MESSAGE CAME ON IN FLIGHT FOR 2 SECONDS. ALARM ALSO WENT OFF AT LAVATORY 1AR THEN WENT OFF AFTER 2 SECONDS. NO SIGN OF FIRE OR SMOKE. PERFORMED SMOKE TEST PER AMM 26-13-00 AND LAVATORY SMOKE DETECTION SELF TEST FOR LAVATORY 1AR PER AMM 26-13-00, BOTH TESTS PASSED. OK FOR SERVICE.