As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT LIT HAD APU FIRE WARNING. CREW FIRED BOTTLE AND RTN TO GATE. UPON FURTHER INVESTIGATION CONTRACT MTC FOUND WHAT APPEARS TO BE A SMALL BURNT SPOT IN INSULATION BLANKET CAUSED BY WHAT APPEARS TO BE A LEAKING FUEL LINE ON APU. CA REMOVED AND REPLACED APU.