As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU CAUSED SMOKE IN THE CABIN WHEN THE ECS WAS TURNED ON. CREW SHUT DOWN THE APU. MAINTENANCE TROUBLESHOT THE ECS SYSTEM AND APU. THIS APU HAS A HISTORY OF STARTING PROBLEMS. THE APU WAS DEFERRED PER MEL 49-10-11 AND RELEASED FOR SERVICE.