As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING CLIMB THE NR 1 ENG FUEL FILTER BYPASS LIGHT ILLUMINATED. THE ACFT RETURNED WHERE MX CARRIED OUT FIM 73-05 TASK 801 & FOUND THE FUEL FILTER DIFFERENTIAL PRESS SWITCH AT FAULT. THE SWITCH WAS REPLACED & SUBSEQUENT ENG RUN CONFIRMED ITS SERVICEABILITY.