As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT FUEL FILTER BYPASS LIGHT ILLUMINATED AFTER ENGINE START. GROUNDED - YES. REF B737-800 AMM 73-34-01-000-801-F00 / 73-34-01-400-801-F00. REMOVED AND REPLACED #1 ENGINE FUEL FILTER DIFFERENTIAL PRESSURE SWITCH. IDLE LEAK CHECK AND EEC TEST PASSED. PERFORMED EEC BITE PROCEDURE B737-800 FIM 73-00-TASK 801 TEST PASSED NO EEC TEST FAULTS.