As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AFTER AUTOBRAKES DISENGAGED, LEFT BRAKE PEDAL DEFLECTION FOR FIRST 3" OF TRAVEL, DOES NOT PRODUCE ANY BRAKING. MAINTENANCE REPLACED THE ALTERNATE BRAKE MASTER CYLINDER AND ACCOMPLIHSED A SATISFACTORY LEAK / OPERATIONAL CHECK PER AMM 32-43-12.