As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 4023 - AFTER RETURNING TO THE GATE, THE CREW REPORTED THE CABIN FILLING WITH SMOKE. MAINTENANCE FOUND AN AIR CYCLE MACHINE SEIZED. THE AIR CYCLE MACHINE WAS REMOVED AND REPLACED IAW EMB MM. OPS CHECK WAS GOOD AND AIRCRAFT WAS RETURNED TO SERVICE. (M)