As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE #1 FIRE WARNING SWITCH WILL NOT ILLUMINATE DURING TEST. (LOOP B WILL NOT TEST, LOOP A TESTS SATISFACTORY). GROUNDED - YES. PERFORMED FIRE DETECTION MODULE BITE. REF B737-900 FIM 26-10 TASK 801, FOUND #1 ENG "B" LOOP FAULT. CLEAN DETECTORS #1 ENG LOWER LOOP FAN AREA. REF B737-900 AMM 26-11-02. FIRE DETECTION SYSTEM OPS CHECKS GOOD. REF AMM 26-11-00.