As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING THE TAXI FROM THE GATE, THE CREW NOTICED A LEFT HAND PACK OVERHEAT LIGHT. THE FLIGHT ATTENDANT THEN REPORTED THERE WAS SMOKE IN THE CABIN. THE CREW RETURNED TO THE GATE AFTER TURNING OFF THE PACKS. MAINTENANCE INSPECTED, CONFIRMED, AND MEL'D THE LEFT HAND HX FAN. FLIGHT 4015 TOOK A THIRTY MINUTE DELAY.