As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 4123 - ENGINE NR 1 LOW N1 ON TAKEOFF, WARNING MESSAGE ON EICAS. ABORTED TAKEOFF. MAINTENANCE FOUND THE ENGINE FAN SPEED SENSOR INOPERATIVE. BOTH ENGINE SENSORS REMOVED AND REPLACED. OPERATIONAL CHECK SATISFACTORY AND AIRCRAFT RETURNED TO SERVICE. REF: OPER CONTROL NR 20000821SH012. (X)