As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
R GEN DRIVE DISC LIGHT UPON START UP TAXI OUT. AIRCRAFT BACK TO BLOCK AND GROUNDED BY MAINTENANCE. MAINTENANCE VERIFIED RIGHT ENGINE OIL SERVICING IAW B767 AMM 12-13-03, NO DEFECTS. REMOVED AND REPLACED RIGHT GCU IAW B767 AMM 24-22-07. BITE AND OPS CHECK GOOD. ACCOMPLISHED IDLE ENGINE RUN IAW B767 AMM 71-00-00. DRIVE LIGHT DID NOT ILLUMINATE WHEN APU SHUTDOWN. A/C REMAINS ETOPS 180. AIRCRAFT RETURNED TO SERVICE