As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER LANDING AND TAXIING AIRCRAFT, APU WAS STARTED & FIRE HANDLE ILLUMINATED & AUDIBLE WAS HEARD. CREW PULLED APU FIRE HANDLE & EMPTY THE APU FIRE BOTTLE. ON FURTHER INVESTIGATION, THE COUPLING FOR THE COMBUSTION LINER BROKE. COUPLING WAS REPLACED. FIRE BOTTLE WAS REPLACED. NO FURTHER PROBLEMS ON SUBSEQUENT FLIGHTS.