As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6150 - IAD-EWR - DURING TAXI, AIRCRAFT RETURNED TO GATE DUE TO LEFT DUCT OVERTEMP LIGHT ILLUMINATED. MAINTENANCE INSPECTED AND FREED PACK. OPS CHECK OK, COULD NOT DUPLICATE. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE (M)