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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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02/12/25

Message Overview:

 Message Name:

APUGCU [VOLTAGE REGULATOR LOW]

Message Code:

2420107LPS

Associated CAS:

APU GEN FAIL
(Advisory)

Reporting LRU: Auxiliary Power Unit (APU) Generator Control Unit (GCU)
System Description: 24-22-00 - Auxiliary AC Power Supply
Schematic Diagram: SSM 24-22-00-101 - Auxiliary AC Power Supply System  [ Global Express ]  [ G5000 ]  [ Global XRS ]
Wiring Diagram: 24-22-00-01 Sheet 1 - Auxiliary AC Power Generation System - 9004-9010 [ Global Express ]  [ G5000 ]  [ Global XRS ]
24-22-00-02 Sheet 1 - Auxiliary AC Power Generation System - 9011-9014 [ Global Express ]  [ G5000 ]  [ Global XRS ]
24-22-00-03 Sheet 1 - Auxiliary AC Power Generation System - 9003, -9015-9158 [ Global Express ]  [ G5000 ]  [ Global XRS] 
24-22-00-04 Sheet 1 - Auxiliary AC Power Generation System - 9002 [ Global Express ]  [ G5000 ]  [ Global XRS] 
24-22-00-01 Sheet 1 - Auxiliary AC Power Generation System -  [ Global Express ]  [ G5000 ]  [ Global XRS ]

Message Description:

Auxiliary Power Unit (APU) Generator Control Unit (GCU) has detected an internal failure related to the voltage regulator low circuit and consequently APU Generator trips off-line.

Possible Causes:

  • Auxiliary Power Unit (APU) Generator Control Unit (GCU) (A109)
  • APU Generator (A110)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Full Throttle Blog/Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

  • The GCU NVMs can only be downloaded at position #2 or #3.
  • A GCU patch cable (GSE REF # 24X-24-02) can be used to swap GCU 1, GCU4 and APU GCU into position 2 or 3 (for troubleshooting only)

Quick Links:

Standard Aircraft Configuration for Maintenance [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM12-00-00-867-801
Aircraft Walkaround (for Maintenance) [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM12-00-00-867-802
Connect Electrical Power to the Aircraft [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-00-00-861-801
Remove the Electrical Power from the Aircraft [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-00-00-861-802
Electrical/Electronic Safety Precautions [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-00-00-910-801
Electrostatic Discharge Safety Precautions [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-00-00-910-802
Removal of the APU Generator [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-22-01-000-801
Installation of the APU Generator [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-22-01-400-801
Operational Test of the APU Generator [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-22-01-710-801
Removal of the Generator Control Units (GCU) [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-24-01-000-801
Installation of the Generator Control Units (GCU) [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-24-01-400-801
Operational Test of the Generator Control Units (GCU) [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM24-24-01-710-801
Access to Active Faults [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM45-45-00-970-802
Access to Stored Faults [ G5000 ]  [ Global Express ]  [ Global XRS ] AMM45-45-00-970-803

Troubleshooting Recommendations:

  1. Remove power from the A/C completely. Apply power back on the A/C and access CAIMS Fault Messages. Is the CAIMS message still present?

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

  2. Interchange AP GCU with GCU 1. Is the fault still present?

    1. If NO, replace APU GCU  and do close out.
    2. If YES, continue with next step.

  3. Disconnect APU Generator connector (A110P1), ACPC connector (A54P4) and APU GCU  connector (A109P1). Perform a continuity check as follows:

    From To Result
    A109P1-J Ground
    A109P1-K Ground
    A109P1-A Ground
    A109P1-B Ground
    A109P1-C Ground

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

  4. Perform a continuity check as follows:

    From To Result
    A109P1-J A110P1-H
    A109P1-K A110P1-B
    A109P1-A A54P4-A
    A109P1-B A54P4-B
    A109P1-C A54P4-C

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

  5. At APU Generator, disconnect G terminal.
  6. Perform a continuity check on aircraft wiring side as follow:

    From To Result
    APU G - G Ground

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

  7. Replace APU Generator (A110).
  8. Do close out.

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