As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT GATE WITH CREW ON BOARD & BEFORE PAX BOARDING, THE CABIN FILLED WITH SMOKE, WHICH MOVED INTO THE JET BRIDGE IN CONJUNCTION WITH A REDUCTION IN APU OIL QTY & FOLLOWED BY APU AUTO SHUTDOWN. R & R APU IAW MCM WC 49-94-11. OPERATIONAL & LEAK CHECKED GOOD. APU ENGINEERING REPORTS OIL LEAK DUE TO ECS-EC CARBON SEAL FAILURE.