04/08/21
Message Overview:
Message Description:
Auxiliary Power Unit (APU)-1 data bus is reported failed by Remote Data Concentrator (RDC) channel A and B. Data Concentrator Unit (DCU) is reporting that the APU display is on.
Possible Causes:
- Auxiliary Power Unit (APU) Electronic Control Unit (ECU) (A39)
- Remote Data Concentrator (RDC) (A13)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin:
- AW300-45-0016 - MDC Nuisance Fault Messages (20500 - 20999)
(This nuisance is corrected in MDT P/N 810-0042-272 and subsequent.)
Forum Articles/Infoservice/Newsletter: None
Quick Links:
| Removal of the Remote Data Concentrator (RDC) | AMM 31-41-05-000-802 |
| Installation of the Remote Data Concentrator (RDC) | AMM 31-41-05-400-802 |
| 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: The APU Master Switch must be selected at RUN (or START) to provide the primary power and the "Essential Operation" command discrete to the APU ECU.
- Reset EICAS RDC A circuit breaker CB1-D2, EICAS RDC B circuit breaker CB2-D2. Is the fault message still present?
- If NO, do close out.
- If YES, continue with next step.
- Do wiring check from RDC (A13) to APU ECU (A39) for the following wires:
From To Result Conn. A13DP1-5A Conn. A39BP1-14A Conn. A13DP1-5B Conn. A39BP1-15A - If the check is satisfactory, continue with next step.
- If the check is not satisfactory, repair wiring.
- Replace RDC (A13). Is the fault message still present\?
- If NO, do close out.
- If YES, continue with next step.
- Replace APU ECU (A39).
- Do close out.