As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER APPLYING BLEED AIR SMOKE WAS COMING OUT OF THE AIR VENTS. SMOKE TOILET CAUTION MESSAGE. OPENED MAIN CABIN DOOR. MESSAGE AND SMOKE CLEARED. (FLT 4553) INSPECTED BOTH PACKS FOR LEAKS AND PROPER OPERATION. OPERATED BOTH PACKS OFF OF THE APU IAW AMM. NO DEFECTS NOTED. INSPECTED THE LAV AREA AND NO EVIDENCE OF SMOKE AND SMOKE DETECTOR SYSTEM OPERATING NORMALLY.