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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:

OPEN CIRCUIT

Message Code:

B3-006328

Associated CAS:

APU FAULT
(Advisory)

Reporting LRU: APU LO OIL PR SW
System Description: 49-00-00
Schematic Diagram: 49-61-00
Wiring Diagram: 49-61-01 Sh 1
49-61-01 Sh 2

Message Description:

The Auxiliary Power Unit (APU) Electronic Control Unit (ECU) is reporting a 'OPEN' circuit of the Low Oil Pressure Switch.

Possible Causes:

  • Low Oil Pressure Switch (S110)
  • 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:

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
Removal of the Low Oil-Pressure Switch AMM 49-91-17-000-801
Installation of the Low Oil-Pressure Switch AMM 49-91-17-400-801
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02

Troubleshooting Recommendations:

  1. Do wiring check from APU ECU (A39) to the Low Oil-Pressure Switch (S110) for the following wires:

    From To Result
    Conn. A39AP1-12A Conn. S110P1-A
    Conn. A39AP1-5D Conn. S110P1-B

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

  2. Replace the Low Oil-Pressure Switch (S110). Is the fault message still present?

    1. If NO, do close out.
    2. If YES, continue with next step.
      NOTE: The switch is a normally closed switch that opens when oil pressure exceeds 35 PSI. The switch closes when pressure drops below 26 PSI.

  3. Replace APU ECU (A39).
  4. Do close out.

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