Message Name:

OPEN PWR/SENSE WIRE
(Service Message)

Message Code:

B3-006335

Associated CAS:

None

Auxiliary Power Unit (APU) Electronic Control Unit (ECU) is reporting an open circuit of the starter motor power cable and/or sense wiring.

• Auxiliary Power Unit (APU) Starter (B4)
• Auxiliary Power Center Primary-Logic (PCB11)
• Auxiliary Power Start Contactor (APSTC) (K62)
• Auxiliary DC Power Center (ADCPC) (A196)
• Auxiliary Power Unit (APU) Electronic Control Unit (ECU) (A39)
• Power Cable
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

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. 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.

2. Do wiring check from the Auxiliary DC Power Center (A196) to APU ECU (A39) for the following wire:

   From	To	Result
   Conn. A196P1-L	Conn. A39AP1-6A

   1. If the check is satisfactory, continue with next step.
   2. If the 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 28 VDC at aircraft positive cable lug (+) of the Starter Motor (B4).

   Measurement at	Expected Result	Result
   aircraft positive cable lug (+)	28 VDC

   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. Confirm presence of the 28 VDC at the Auxiliary DC Power Center (A196).

   Measurement at	Expected Result	Result
   Conn. A196 STUD-T2	28 VDC

   1. If the check is satisfactory, continue with next step.
   2. If the check is not satisfactory, verify in the MDC for ATA 24 message faults and continue with respective troubleshooting.

7. Disconnect the Auxiliary Power Center Start Contactor (K62) connector. Do visual inspection of the connectors and associated wiring for any loose pins and/or damaged wire.

   1. If inspection is satisfactory, continue with next step.
   2. If inspection is not satisfactory, go to step 12.

8. Verify Auxiliary Power Center Start Contactor (K62) coils by measuring the resistances at the contactor connector (J-side) as per the following table:

   Coils	Expected Values	Results
   Pin 1 and Pin 2 (Pick-up)	between 4.5 Ω and 6.5 Ω
   Pin 2 and Pin 3 (Hold)	between 260 Ω and 280 Ω

   1. If the verification is satisfactory, continue with next step.
   2. If the verification is not satisfactory, replace the defective Auxiliary Power Center Start Contactor (K62).
      NOTE: It is important to not skip this verification before proceeding with the swap at step 9. A short of one of the 2 coils will result with a blowing of a fuse the Auxiliary Power Center Primary-Logic (PCB11).

9. Swap Contactor K62 with contactor K71 or K72 (both located in ADCPC). Is the fault message still present\?

   1. If YES, continue with next step.
   2. If NO, replace defective Contactor K62.

10. Replace APU ECU (A39). Is the fault message still present?

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

11. Replace Auxiliary Power Center Primary-Logic (PCB11). Is the fault message still present?

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

12. Replace Auxiliary DC Power Center (A196).
13. Do close out.