As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT RSV BRAKE VAL EICAS MEESAGE CAME ON . AC RETURNED TO GATE AND MAINTENACE GROUNDED AC AND T/S PER FIM 29-11 FT 828. VERIFIED NO PWR TO C2 ISOLATED ACMP SUPPLY SOV. K1 RELAY ON M1216 PANEL BAD. REPLACED PANEL PER WDM 29-21-32. OPS CHECK GOOD AND RETURNED AC TO SERVICE .