As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT THE GATE JUST PRIOR TO DEPARTURE, WHEN THE AIR-CONDITIONING SUPPLY SWITCHES WERE PLACED ON, THE FLIGHT ATTENDANTS NOTICED HAZE AND SMOKE ODOR IN THE AFT CABIN. MAINTENANCE FOUND THE APU OIL CAP OFF AND OIL AROUND THE APU RAM AIR DOOR INLET. APU AND INLET CLEANED. DUCT BURNOUT PERFORMED, COALESCER BAGS REPLACED. NO FURTHER HAZE OR ODOR PRESENT. A/C RETURNED TO SERVICE.