As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INBOUND TO MSN, THE NR 2 FIRE WARNING ILLUMINATED. SYSTEM FAILED OPERATIONAL TEST OF THE SECONDARY LOOP. PULLED THE FIRE HANDLE SHUTTING DOWN NR 2 AND DISCHARGED BOTH FIRE BOTTLES. FOUND 'B' LOOP HAD MALFUNCTIONED. PLACED THE 'B' LOOP ON MEL. INSPECTED ENGINE FOR PNEUMATIC LEAKS. NONE FOUND. REPLACED THE FIRE BOTTLES. ENGINE RUN-UP AND SYSTEM CHECKED OK. AIRCRAFT RETURNED TO SERVICE.