As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT LH ISLV VALVE STUCK IN CLOSED POSITION ,AC RETURNED TO GATE (BTB) AND MTX GROUNDED AC . PERFORMED OPS L ISLN VALVE CHRECKD WITH NO NO ISSUES FOUND CYCLE IT SEVERAL TIMES VALVE OPERATED OK IAW AMM 36-11-04. AIRCRAFT REMAINS ETOPS 180. MTX RETURNED AC TO SERVICE .