As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DESCENDING BELOW 4000 FEET FUMES IN FLIGHT DECK ONLY. FUMES WERE PRESENT THROUGH LANDING AND TAXI. FLIGHT CREW DONNED OXYGEN MASKS ON TAXI IN. MAINTENANCE REPLACED THE LEFT CABIN RECIRCULATION FAN AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 21-21-51.