Message Name:

FIRE WARN O/P DISCRETE

Message Code:

B3-006751

Associated CAS:

FIRE SYS FAULT
(Advisory)

Fault in FIREX Control Unit (CU) FIRE WRANING discrete output to Data Concentrator Unit (DCU). FIREX CU fault or wiring problem (wire open or short, or driver has failed) for LEFT or RIGHT ENGINE, APU FIRE, or MAIN WHEEL WELL OVERHEAT WARNING DISCRETES.

• Fire-Detection-and-Extinguishing Control Unit (FIREX CU) (A91)
• Data Concentrator Unit (DCU) (A14)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

1. Check the FIREX Control Unit (A91) circuit breaker CB1-A11, CB2-A11 pull and reset, recheck MDC for the fault.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

2. Perform wiring check FIREX discrete outputs for continuity and no shorts to ground to the DCU (repair as required).

   1. Left engine fire discrete, FIREX Control Unit A91P1 pin 48 to DCU A14BP1 pin 5E.
   2. Right engine fire discrete, FIREX Control Unit A91P2 pin 48 to DCU A14EP1 pin 7J.
   3. APU fire discrete, FIREX Control Unit A91P1 pin 29 to DCU A14EP1 pin 8J.
   4. MWW fire discrete, FIREX Control Unit A91P3 pin 25 to DCU A14EP1 pin 13J.

      1. If system checks are good, do close out.
      2. If fault remains, continue with next step.

3. Replace FIREX control unit.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

4. Replace DCU.
5. Do close out.