As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INFLIGHT SJD TO ORD. FLIGHT CREW REPORTED HEAVY SMELL OF ELECTRICAL FUMES IN AFT CABIN AFTER TURNING ON AIRFOIL ANTI ICE TO FULL. DIVERTED TO STL DUE TO CHANCE OF ICING IN ORD AND LANDED WITHOUT INCIDENT. ACCOMPLISHED AIR CONDITIONING PACK BURNOUT AND REPLACED BOTH LEFT AND RIGHT PRESSURE REGULATING VALVES IN TAIL SECTION. NO FUMES DURING FUNCTIONAL FLIGHT CHECK.