As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SITTING ON RAMP MASSIVE AMOUNTS OF SMOKE COMING FROM APU EXHAUST. SHUT APU DOWN & DISCHARGED APU FIRE BOTTLE. NO FLAMES SEEN OR REPORTED. THERE WERE NO COCKPIT INDICATIONS OF FIRE. PERFORMED APU RUN. APU PERFORMED SATISFACTORY. REMOVED & REPLACED THE LT FIRE BOTTLE AND TESTED IAW CMP CARDS 262020 AND 262424. TESTED SATISFACTORY.