As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FUMES OF UNKNOWN ORIGIN IN MAIN CABIN REPORTED BY ALL FLIGHT ATTENDANTS MORE PREVLENT AT ROW 33. ODOR WAS NOT ELECTRICAL, FUEL OR EXHAUST RELATED. RETURNED TO GATE. THE AIRCRAFT WAS GROUNDED. ACCOMPLISHED TROUBLESHOOTING IAW CARD 05-96-84, AND CARD 05-96-86. ALSO REPLACED THE CABIN RECIRCULATING FILTERS IAW AMM 210-21-41 AND LEFT AND RIGHT OZONE FILTERS IAW AMM 21-51-41. ALL CHECKED NORMAL.