As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CAPTAIN REPORTED THAT AFTER RT ENGINE START, THE FILTER BYPASS LIGHT TURNED ON; SO THE FLIGHT CREW PERFORMED THE QRH 12.8 PROCEDURE, CONFIRMING THE FAILURE RETURNING TO THE GATE. DURING MX REVISION, THE MESSAGE 73-31072 SHOWED; SO THE REPORT WAS DEFERRED IAW MEL 73-4-2 CAT C AND ACFT WAS DISPATCHED IN SUCH CONDITION. MX REPLACED THE FUEL DIFFERENTIAL PRESSURE SWITCH AND FILTER IAW MM 73-34-01 AND MM 73-11-02, TESTED CORRECT.