As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT CREW PERSONNEL REPORTED SMOKE IN THE CABIN AFTER TURNING ON APU AIR AT THE GATE. MAINTENANCE DEPARTMENT PERSONNEL INSPECTED AND FOUND HYD FLUID LEAKING FROM LEFT REVERSER CONTROL VALVE INJESTED INTO APU INLET CAUSING SMOKE IN CABIN THROUGH THE AIR SYSTEM. RESECURED NUT ON VALVE, LEAK CHECK GOOD IAW AMM 78-31-03. AIRCRAFT RETURNED TO SERVICE.