As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT CREW ADVISED DISPATCH OF FUMES IN THE COCKPIT (POSSIBLY DUE TO AN EXTRACT FAN OVERHEAT). CREW ON OXYGEN. DECLARED EMERGENCY FOR EXPEDITED LANDING AT ORD ON 14L. EXTRACT FAN OVERHEATED. NO REPORTED APU PROBLEMS. EXTRACT FAN REPLACED PER MM 21-26-51. REPLACEMENT FAN OPERATES OK.