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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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06/04/21

Message Overview:

Message Name:

SHORT/LO PWR INPUT

Message Code:

B3-006336

Associated CAS:

None

Reporting LRU: APU START MOTOR
System Description: 49-00-00
Schematic Diagram: 49-61-00
24-61-00
Wiring Diagram: 49-61-01 Sh 1
49-61-01 Sh 2
24-61-03

Message Description:

Auxiliary Power Unit (APU) Electronic Control Unit (ECU) is reporting that the starter motor voltage is less than 10 VDC with the start contractor energized.

Possible Causes:

  • Right Battery (BT2)
  • Auxiliary Power Unit (APU) Starter (B4)
  • Auxiliary Power Unit (APU) Electronic Control Unit (ECU) (A39)
  • Right DC Power-Center (R DCPC) (A36) L DCPC ESS BUS 5 Amp Circuit Breaker (CB6−C1)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Notice To Operators (NTO): None

Flight Operation Notifications Manual (FONM): None

NOTE: Check Right DC Power-Center (R DCPC) (A36) L DCPC ESS BUS 5 Amp Circuit Breaker (CB6−C1) first.

Quick Links:

Removal of the Battery AMM 24-32-01-000-801
Installation of the Battery AMM 24-32-01-400-801
Restoration (Bench Check) of the Batteries AMM 24-32-01-610-801
Operational Test of the Batteries AMM 24-32-01-710-801
Detailed Inspection of the APU Starter Brushes AMM 49-42-00-220-801
Removal of the Starter Motor AMM 49-42-01-000-801
Installation of the Starter Motor AMM 49-42-01-400-801
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: 1: The APU Master Switch must be selected at RUN (or START) to provide the primary power to the APU ECU.

NOTE: 2: The APU Master Switch must be selected at START to provide the power at the Starter Motor.

  1. Energize the Aircraft with the right Battery only and confirm voltage does not abnormally decreased.

    1. If right Battery holds voltage, continue with next step.
    2. If right Battery does not hold voltage, remove and service battery.

  2. Confirm presence of the Start Voltage reference at the APU ECU (A39).

    Measurement at Expected Result Result
    Conn. A39AP1-7A Aircraft Ground

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

  3. Remove the aircraft positive cable lug (+) from the positive terminal of the Starter Motor (B4).
  4. Confirm presence of the right battery voltage at aircraft positive cable lug (+) of the Starter Motor (B4).

    Measurement at Expected Result Result
    aircraft positive cable lug (+) 28 VDC or current battery voltage

    1. If the check is satisfactory, replace defective Starter Motor (B4).
    2. If the check is not satisfactory, continue with next step.

  5. Do wiring check from the Auxiliary DC Power Center (A196) to aircraft positive cable lug (+) of the Starter Motor (B4) for the following cable:

    From To Result
    Conn. A196P1 STUD-T9 aircraft positive cable lug (+)

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

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

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