As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EICAS MESSAGE C HYD PRIM 1 ON TAXI OUT. AIRCRAFT BACK TO BLOCK AND GROUNDED BY MAINTENANCE. MAINTENANCE PERFORMED OPERATIONAL TEST AND IDLE ENG RUN NO DEFECTS NOTED AT THIS TIME IAW B767 29-11-00, 71-00-00 AMM. AIRCRAFT RETURNED TO SERVICE.