As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT WITH ONE ENGINE OPERATING AND APU OPERATING, SMOKE BEGAN TO FILL THE CABIN. AFTER BOTH PACKS TURNED OFF, SMOKE BEGAN TO CLEAR. RETURNED TO GATE. FOUND OIL LEAKING FROM APU COMPARTMENT AND DRIPPING IN VICINITY OF APU AIR INTAKE. APU AIR INLET SATURATED WITH OIL. CLEANED INLET, PERFORMED DUCT BURNOUT.