As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI AS PACKS NR 2 AND NR 3 WERE BROUGHT ON LINE, SMOKE BEGAN TO ENTER THE CABIN AREA. AIRCRAFT RETURNED TO THE GATE AND PASSENGERS DEPLANED THROUGH THE JETWAY. MAINTENANCE FOUND OIL CONTAMINATION FROM THE APU WAS THE SOUCE OF SMOKE. PACK/DUCTING BURN OUT PROCEDURE C/W AND COALESCER BAGS WERE REPLACED. APU WAS PLACED ON MEL.