As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED THAT DURING TAXI RECEIVED A BRAKE DEGRADED MESSAGE ON THE EICAS AND NOTED THAT THE BRAKES FELT SPONGY AND UNRESPONSIVE. THE CREW RETURNED TO THE GATE WITHOUT INCIDENT. MAINTENANCE FOUND AIR IN THE BRAKE SYSTEM AND BLED ALL FOUR BRAKES. OPERATIONAL CHECKS WERE GOOD WITH NOT FURTHER DEFECTS NOTED AT THAT TIME.