04/08/21
Message Overview:
Message Description:
Auxiliary Power Unit (APU) protective shutdown - loss of overspeed protection.
Possible Causes:
- Auxiliary Power Unit (APU) Speed Sensor (MT116)
- Auxiliary Power Unit (APU) Electronic Control Unit (ECU) (A39)
- Fuel Control Unit (FCU)
- Fuel Solenoid Valve (SOV) (HP8)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin: None
Forum Articles/Infoservice/Newsletter: None
Fault Confirmation Procedure:
- Message# = 2
- {Term Definitions}
- APU-37 XX 352 01 EXCT XXXX-XXXX XXXX-TXXX XXXX-XXXX 352:20; APU S/D LOSS OVSP PROT.
Quick Links:
| Removal of the Fuel Control Unit | AMM 49-31-01-000-801 |
| Installation of the Fuel Control Unit | AMM 49-31-01-400-801 |
| Removal of the Fuel Solenoid Valve | AMM 49-31-09-000-801 |
| Installation of the Fuel Solenoid Valve | AMM 49-31-09-400-801 |
| 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 |
| Removal of the Speed Sensor | AMM 49-61-13-000-801 |
| Installationof the Speed Sensor | AMM 49-61-13-400-801 |
| Wiring - Maintenance Practices - ALL | SPM 20-12-00-02 |
| Wire Repair - Maintenance Practices - ALL | SPM 20-12-10-02 |
Troubleshooting Recommendations:
- APU protective shutdown - loss of overspeed protection. Condition due to a combination of speed sensor, ECU, and/or FCU SOV solenoid.