As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL - FLIGHT#3740. CREW REPORTED A BURNING SMELL IN COCKPIT. MAINTENANCE INSPECTED ALL ELECTRICAL EQUIPMENT IN COCKPIT AND COULD NOT FIND ANY DEFECTS. AFTER INSPECTING THE COCKPIT ZONE SENSOR IT WAS FOUND TO BE OVERHEATED. ZONE SENSOR REPLACED, NO FURTHER ODORS DETECTED. AIRCRAFT RETURNED TO SERVICE.