As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT, AFTER STARTING ENGINES THE A-SYSTEM HYD QUANTITY WENT TO .125 WITH LOW QTY LIGHT ON. SYSTEM PRESSURE WAS OK. DEPRESSURIZED SYSTEM AND RETURNED TO GATE. FOUND THE LEFT INBOARD AILERON THE OUTBOARD ACTUATOR HAD FAILED ALSO BREAKING ONE OF THE 3 HYD LINES CONNECTED TO ACTUATOR.