As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT WHILE STARTING #2 ENGINE ,#2 ENGINE START VALVE WILL NOT OPEN DURING START. A/C RETURNED TO GATE (BTB) AND MTX GROUNDED A/C. MTX DEFERRED #2 START VALVE IAW MEL ABX-80-00-2-1.AC RELEASED NO ETOPS .AND RETURNED A/C TO SERVICE.