As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTS #1 ENG FIRE DET SYS WON'T TEST. GROUNDED - YES. PER B737-800 FIM 26-10 TASK 801 AND 805 INITIAL EVALUATION: FIRE DETECT CTR MODULE BITE SHOWS ENG 1 LOOP B OPEN. FOUND WIRES LOOSE IN LUGS AT DETECTOR 4 AFT (HARNESS MW0326). REPAIRED BOTH TERMINAL LUGS IAW EA 800-26EA-23297 AND B737-800 AMM 23-11-02-960-802. FIRE CTR MODULE BITE AND FIRE WARNING TEST GOOD. REPAIR CONFIRMATION SUCCESSFUL.