As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RESERVE BRK VALVE EICAS DURING TAXI OUT, VALVE LT ON SWITCH ON AND ISO VLV LT ON ACC PANEL ON, SW OFF. AIRCRAFT BACK TO BLOCK AND GROUNDED BY MAINTENANCE. MAINTENANCE PERFORMED TEST TO ISOLATE C1 ACMPCENTER SYSTEM PER AMM 29-11-00, ISOLATED ACMP SUPPLY SHUTOFF VALVE WOULD NOT INDICATE IN DISAGREE. REMOVED AND REPLACED ISOLATED ACMP SUPPLY SHUTOFF VALVE IAW AMM 29-11-07. OPS CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.