As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ASA TSR713760 FOUND ENG 1 FAULT 73-44632 FAN SPEED N1 SENSOR LOW TOOTH SIGNAL IS INVALID DETECTED BY ENG 1 EEC CH. B UNDER PRESENT LEG FAULTS/ FAULT HISTORY LEGS 0,3,4 AND 16. GROUNDED - YES. REMOVED AND REPLACED #1 ENG N1 SENSOR REF B737-9 AMM 77-12-01.