As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT LEFT ENGINE FIRE WARNING LIGHT ILLUMINATED, DETERMINED NO FIRE EXISTED, LANDED AIRCRAFT OAKLAND IAP. MAINTENANCE DETERMINED FIRE DETECTOR WAS MALFUNCTIONING REPLACED THE LOWER NR 1 ENGINE FIREWALL DETECTOR SYSTEM OPERATIONAL TESTS SATISFACTORY.