As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING INITIAL TAKEOFF ROLL AT APPROXIMATELY 40 KNOTS, FLIGHT CREW RECEIVED A MASTER CAUTION WARNING. FLIGHT CREW APPLIED BRAKES WITH ANTISKID SYSTEM ON AND THERE WAS NO BRAKE PRESSURE. TURNED ANTISKID SYSTEM OFF AND BRAKE PRESSURE WAS AVAILABLE. AIRCRAFT STOPPED AND RETURNED TO GATE. REPLACED BRAKE VALVE IAW MM 32-42, OPS CHECKED OK.