As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURN BACK AT 1244, FLIGHT CREW REPORTED VENT EXTRACT FAULT. AIRCRAFT RETURNED TO KMDW AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AIRCRAFT AND PERFORMED OPS SYSTEM TEST VIA MCDU. NO DISCREPANCIES NOTED. AIRCRAFT OKAY FOR SERVICE IAW AMM 21-26-00-710-050.