As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FIRE DETECTION TEST FAULT ENGINE #1. GROUNDED - YES. THE SYSTEM STARTED TESTING PROPERLY, PROBLEM IS INTERMITTENT. THE ENG/APU FIRE DETECTOR MODULE PREVIOUSLY HAD A LOWER FAN DETECTOR FAULT. REMOVED AND REPLACED LOWER FAN FIRE DETECTOR HARNESS IAW B737-800 AMM 26-11-02-000-801 AND 26-11-02-400-801.