As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
C HYD PRIM 1 EICAS MESSAGE DURING PUSHBACK AND AC RETURNED TO GATE (BTB), MTX GROUNDED AC AND BEGAN TROUBLESHOOTING. PERFORMED T/S IAW FIM 29-11 FT 810. FOUND THE TIME DELAY M303 FAULTY. REPLACED TIME DELAY MODULES M303 AND M304 IAW WDM 29-11-31. CENTER HYD SYSTEM OPS CHECK GOOD IAW AMM 29-11-00/501. AIRCRAFT RETURNED TO SERVICE.