As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT DURING ENGINE #2 START WITH AUTO SELECTED, START VALVE LIGHT ILLUMINATED BUT NO ROTATION.AC RETURNED TO GATE (BTB) AND MTX GROUNDED AC . MTX DEFERRED THE #2 START VALVE IAW MEL ABX-80-00-2-1. . AC REMAINS ETOPS 180 AND RETURNED AC TO SERVICE.