As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CAPTAIN REPORTED THICK SMOKE AND ODOR COMING OUT OF VENTS ON GROUND WHEN HE TURNED ON THE APU. FLIGHT ATTENDANTS REPORTED FEELING WOOZY - NO PASSENGERS WERE ON THE PLANE YET. MAINTENANCE PLACED THE APU ON MEL. MAINTENANCE TROUBLESHOT WITH NO LEAKS OR DEFECT NOTED. PERFORMED ECS DECONTAMINATION.