As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SMOKE WARNING LIGHT ILLUMINATED. AIRCRAFT RETURNED TO PDX AND MADE AN UNEVENTFUL LANDING. MAINTENANCE INSPECTED THE AIRCRAFT AND FOUND NO EVIDENCE OF SMOKE OR FIRE. REPLACED BOTH SMOKE DETECTORS IN THE CARGO COMPARTMENT, OPERATIONAL CHECKS GOOD.