As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU WAS ON WHEN ARRIVING AT AIRCRAFT. SOON AFTER WE ARRIVED THE APU AUTO SHUTDOWN AND APU SHOWED APU FAIL LIGHT. AFTER COMPLETING THE CHECKLIST, WE GAVE THE APU 10 MINUTES AND STARTED THE BLEED AIR. THE COCKPIT FILLED WITH SMOKE. WE SHUT DOWN THE APU AND TURNED OFF THE RECIRC FAN. REMOVED FROM SERVICE. PLACED THE APU ON MEL 49-00-1.