As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT RETURNED TO THE GATE WHEN DURING THE TAXI OUT THE CREW RECEIVED A RT PACK MASTER CAUTION. MAINTENANCE INSPECTED THE AIRCRAFT AND REPLACED THE RT PACK TEMPERATURE CONTROL VALVE. OPERATIONAL AND LEAK CHECKS WERE GOOD AND THE AIRCRAFT WAS RETURNED TO SERVICE.