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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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04/08/21

Message Overview:

Message Name:

OPN/SHRT IGN EXCITER

Message Code:

B3-006326

Associated CAS:

None

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

Message Description:

Open or short circuit of the ignition unit exciter and/or wiring.

Possible Causes:

  • Auxiliary Power Unit (APU) Electronic Control Unit (ECU) (A39)
  • Ignition Unit (A173)
  • Igniter Plug
  • APU Wire Harness
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin:

Forum Articles/Infoservice/Newsletter:

The ignition unit fault is a nuisance caused by the Built-in-Test (BIT) limits in the APU ECU. Should be ignored unless the APU is experiencing light-off problems accompanied by a no flame shut-down fault.

Refer to Honeywell SIL D201008000031 "Nuisance Ignition Faults".

Quick Links:

Operational Test of the Auxiliary Power Unit (APU) AMM 49-11-01-710-801
Removal of the Ignition Unit AMM 49-41-01-000-801
Installation of the Ignition Unit AMM 49-41-01-400-801
Detailed Inspection of the APU Igniter Plug AMM 49-41-09-220-801
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
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02

Troubleshooting Recommendations:

  1. Do Operational Test of the Auxiliary Power Unit.

    1. If the test is satisfactory, consider this fault message as a nuisance fault and do close out.
    2. If the test is not satisfactory, continue with next step.

  2. When the start is attempted, can you hear the "ticking" sound of the igniters?

    1. If YES, go to step 5.
    2. If NO, continue with next step.

  3. Remove the APU ECU. Disconnect the Ignition Unit connector A173P1. Perform a continuity check as follows:

    From To Result
    A39CP1-2 A173P1-B
    A39CP1-4 A173P1-A

    1. If there is continuity, continue with next step.
    2. If there is no continuity, repair defective wiring as required and do close out.

  4. Perform a continuity check as follows:

    From To Result
    A39CP1-2 Ground
    A39CP1-4 Ground

    1. If there is no continuity, replace the Ignition Unit.
    2. If there is continuity, repair defective wiring as required and do close out.

  5. Perform a detailed inspection of the APU igniter plug as per AMM 49-41-09-220-801. Check for erosion and gaps.

    1. If defects are found, replace the igniter plug and do close out.
    2. If no defects are found, continue with next step.

  6. Replace Ignition Unit (A173). Is the fault message still present?

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

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

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