As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT ATC NOT RECEIVING INFO FROM EITHER XPDR . NO EICAS MSG. AC RETURNED TO THE GATE AND MAINTENANCE GROUNDED AC AND PERFORMED OPS CHECK IAW B767 AMM 34-5302 AND ATC WAS PICKING UP SIGNAL NOW AND WAS OPERATING NORMALLY. MAINTENANCE RETURED AC TO SERVICE AND DEPARTED .