As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO BLOCKS DUE TO AN ELECTRICAL BURNING ODOR AFTER LEFT ENGINE START. ODOR DISSIPATED. DURING TAXI TO GATE ELECTRICAL ODOR BECAME STRONGER. COMPLETED TOUBLESHOOTING IAW FIM. NO FINDINGS. PERFORMED DUCT BURNOUT IAW AMM. RAN ENGINES FOR 50 MINUTES. NO FUMES OF ANY TYPE.