As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAH - FLIGHT 2156 - AFTER TAKEOFF THE LAVATORY SMOKE INDICATOR WARNING LIGHT ILLUMINATED. THE AIRCRAFT RETURNED TO IAH AND LANDED WITHOUT INCIDENT. UPON INSPECTION THE NR 2 ENGINE WAS FOUND TO BE THE SOURCE OF THE SMOKE. MAINTENANCE REMOVED AND REPLACED THE NR 2 ENGINE, PERFORMED GROUND RUNS AND CLEARED THE DISCREPANCY.