As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT 959 ON FLIGHT 5001 FROM HTS TO CLT. DURING TAXI OUT FOR DEPARTURE AT HTS THE LEFT BRAKE PRESSURE INDICATED ZERO AND THE LEFT BRAKE DID NOT RESPOND TO PEDAL INPUT. NO EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO THE GATE WITH NO OTHER PROBLEMS. MAINTENANCE FROM CLT TIGHTENED LOOSE WIRE ON THE BRAKE PRESSURE TRANSMITTER. THE LEFT BRAKE SHUTTLE VALVE WAS FOUND TO BE LEAKING. MAINTENANCE REMOVED AND REPLACED THE SHUTTLE VALVE. OPS CHECK WAS GOOD. AIRCRAFT RETURNED TO SERVICE.