As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAIN DECK CARGO SMOKE DETECTOR ZONE 4 LIGHT CAME ON ALONG WITH THE CARGO FIRE LIGHT AND BELL. AFTER 20 MINUTES THE LIGHTS WENT OUT. TESTED SYSTEM AND TEST OK. MAINTENANCE CLEANED PLUG ON DETECTOR AND TEST OK. OPERATIONAL CHECKED GOOD AND AIRCRAFT WAS RETURNED TO SERVICE.