01/28/21
Message Overview:
Message Description:
The amber 'APU STARTER FAIL ON' caution CAS message indicates power is still being supplied to the APU starter when the electronic control unit (ECU) is not commanding a start.
- The APU ECU is reporting that the Start Contactor did not disengaged.
Possible Causes:
- Auxiliary Power Start Contractor (APSTC) (K62)
- Auxiliary Power Unit (APU) Electronic Control Unit (ECU) (A39)
- Auxiliary Power Center Primary-Logic (PCB11)
- Auxiliary DC Power Center (Aux DCPC) (A196)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin: None
Forum Articles/Infoservice/Newsletter: None
Quick Links:
| Removal of the Auxiliary DC Power Center (Aux DCPC) | AMM 24-64-01-000-801 |
| Installation of the Auxiliary DC Power Center (Aux DCPC) | AMM 24-64-01-400-801 |
| Removal of the Auxiliary DC Power Start Contactor | AMM 24-64-05-000-801 |
| Installation of the Auxiliary DC Power Start Contactor | AMM 24-64-05-400-801 |
| Removal of the Auxiliary Power Center Primary-Logic | AMM 24-64-13-000-801 |
| Installation of the Auxiliary Power Center Primary-Logic | AMM 24-64-13-400-801 |
| 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 |
| Standard Practices - Replace Wiring | SPM 20-12-00-02 |
| Electrical Bonding - Maintenance Practices | SPM 51-80-00-02 |
| 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.
- Do wiring check from the Auxiliary DC Power Center (A196) to APU ECU (A39) for the following wire:
From To Result Conn. A196P1 - Y Conn. A39BP1 - 1B - If the check is satisfactory, continue with next step.
- If the check is not satisfactory, repair defective wiring.
- 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.
- If inspection is satisfactory, continue with next step.
- If inspection is not satisfactory, go to step 6.
- Verify Auxiliary Power Center Start Contactor (K62)main contacts by measuring the resistances at the contactor connector (J-side) as per the following table:
Measurement at: Expected Results Results Main contact #1 and Main contact #2 Open - If the verification is satisfactory, continue with next step.
- If the verification is not satisfactory, replace the defective Auxiliary Power Center Start Contactor (K62).
- Replace APU ECU (A39). Is the fault message still present?
- If YES, continue with next step.
- If NO, do close out.
- Replace Auxiliary Power Center Primary-Logic (PCB11). Is the fault message still present?
- If YES, continue with next step.
- If NO, do close out.
- Replace Auxiliary DC Power Center (A196).
- Do close out.