As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD FLT 6051 - THE CREW REPORTED WHILE SITTING ON GROUND, PACK 2 WAS SET TO MANUAL MODE TO EXPEDITE COOLING THE CABIN AND COCKPIT FILLED WITH SMOKE. THE APU BLEED WAS OPEN. MAINTENANCE INSPECTED AND PERFORMED OPERATIONAL CHECKS OF THE APU AND PACK SYSTEMS. NO SMOKE WAS NOTED AND THE AIRCRAFT WAS RELEASED FOR SERVICE.