As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PREFLIGHT CHECK. EMERGENCY BRAKE PRESSURE FOUND TO BE ZERO. PERFORMED A PRESSURE RECHARGE PROCEDURE. WITH PARK BRAKE SET THE EMERGENCY BRAKE PRESSURE CONTINUED TO BLEED DOWN. WITH PARK BRAKE RELEASED THE EMERGENCY BRAKE PRESSURE DECREASED RAPIDLY. REPLACED THE EMERGENCY PARKING BRAKE VALVE.