As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ATTEMPTED TO START THE APU AFTER LANDING WHILE TAXIING & RECEIVED A RT ESS BUSS FAULT CAS & AN APU FAIL CAS, AFTER ENG SHUTDOWN. THE RT BATTERY COULD NOT BE SHUTOFF. FORCED TO DISCONNECT THE BATTERY CABLES. TROUBLESHOOTING FOUND THE RT AFT PDP DEFECTIVE & REPLACED IT WITH REPAIRED UNIT. OPERATIONS CHECKS SATISFACTORY.