As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 4062 - DURING CRUISE FLIGHT, LAVATORY SMOKE ILLUMINATED. CREW NOTED SOME KIND OF VAPOR OR MIST IN CABIN. MAINTENANCE TROUBLESHOT TO APU INTRODUCING VAPOR INTO THE APU BLEED WHICH ACTIVATED THE LAVATORY SMOKE DETECTOR. APU PUT ON MEL. REMOVED AND REPLACED APU. OPERATIONAL CHECK SATISFACTORY AND AIRCRAFT WAS RETURNED TO SERVICE. (M)