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(WARNING)
RED MESSAGE (CAUTION)
AMBER MESSAGE (ADVISORY)
CYAN MESSAGE (STATUS)
WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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Quick Links

04/08/21

Message Overview:

Message Name:

NO BATT BUS PWR
(Service Message)

Message Name:

B3-006324

Associated CAS:

None

Reporting LRU: APU ECU
System Description: 49-00-00
Schematic Diagram: 49-61-00
Wiring Diagram: 49-61-01 Sh 1
49-61-01 Sh 2

Message Description:

Secondary voltage to Auxiliary Power Unit (APU) Electronic Control Unit (ECU) less than 10 VDC.

Possible Causes:

  • Auxiliary Power Unit (APU) SEC CONTROL Circuit Breaker (CB2-B8)
  • Right Cockpit Circuit Breaker Panel (CBP2)
  • Auxiliary Power Unit (APU) Electronic Control Unit (ECU) (A39)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Replacement of DC Circuit Breakers AMM 24-65-00-960-801
Removal of the Cockpit Circuit-Breaker Panel (CCBP) AMM 24-65-01-000-801
Installation of the Cockpit Circuit-Breaker Panel (CCBP) AMM 24-65-01-400-801
Removal of the Auxiliary Power Unit (APU) Electronic Control Unit (ECU) AMM 49-61-01-000-801
Installation of the Auxiliary Power Unit (APU) Electronic Control Unit (ECU) AMM 49-61-01-400-801
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02

Troubleshooting Recommendations:

NOTE: The APU Master Switch must be selected at RUN (or START) to provide the primary power and the "Essential Operation" command discrete to the APU ECU.

  1. Confirm presence of the Ground (Secondary Power) at the APU ECU (A39).

    Measurement at Expected Result Result
    Conn. A39CP1-3 Aircraft Ground

    1. If check is satisfactory, continue with next step.
    2. If check is not satisfactory, repair defective wiring.

  2. Confirm presence of the 28 VDC (Secondary Power) at the APU ECU (A39).

    Measurement at Expected Result Result
    Conn. A39CP1-5 28 VDC

    1. If check is satisfactory, go to step 6.
    2. If check is not satisfactory, continue with next step.

  3. Do wiring check from the right Cockpit Circuit-Breaker Panel (CBP2) to APU ECU (A39) for the following wires:

    From To Result
    Conn. CBP2J2-V Conn. A39CP1-5

    1. If the check is satisfactory, continue with next step.
    2. If the check is not satisfactory, repair defective wiring.

  4. Replace APU SEC CONTROL Circuit Breaker CB2-B8. Is the fault message is still present?

    1. If NO, do close out.
    2. If YES, continue with next step.

  5. Replace right Cockpit Circuit-Breaker Panel (CBP2). Is the fault message is still present?

    1. If NO, do close out.
    2. If YES, continue with next step.

  6. Replace APU ECU (A39).
  7. Do close out.

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