Fault Message:

APU GEN HIGH OIL TEMP

Fault Code:

4960135APU

Associated CAS:

APU SHUTDOWN
(Advisory)

The Full-Authority Digital Engine-Controller (FADEC) stopped the Auxiliary Power Unit (APU) because there was an APU Generator over temperature condition (more than 215±5°C for more than 1.25±0.25 seconds) detected on the ground in the non-essential mode.

• Auxiliary Power Unit (APU) Generator (A110)
• Auxiliary Power Unit (APU) Generator Control Unit (GCU) (A109)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

If the CAS message APU OIL HI TEMP or the CAIMS message HIGH OIL TEMPERATURE (4960124APU) has also been displayed or recorded, first perform troubleshooting for this condition/fault.

If CAS message is not active, verify stored flight faults on CAIMS, under system diagnostics, ATA 49.

• The Thermostatic/Pressure Relief Valve is normally a non field replaceable item. It will be included in the Oil Cooler Assembly
• The Generator Temperator Sensor is not a field replaceable item. It will be included in the Auxillary Generator Assembly

The oil from the APU gearbox keeps the generator cool. The oil flows through APU generator and gearbox to the center of the rotor shaft and out through jets as a spray. The oil keeps the coils and diodes cool and it also lubricates the bearings of the APU generator. The oil falls from the coils and collects in two sumps installed at each end of the generator. The oil is sent back to the APU gearbox, through the cooling and filtration system, by an external scavenge pump.

The APU generator has a temperature sensor that can sense if there is over-temperature. If there is over-temperature, the sensor sends a signal to the GCU. The GCU sends a signal to the DAU through the ARINC 429 data bus.

1. Visually check the oil quantity in the APU. Inspect for oil leakage at the APU or APU Generator.

   1. If APU oil level was low, investigate absence of APU OIL LO QTY, CAS (Cyan) message.
   2. If system checks are good, do close out.
   3. If fault remains, continue with next step.

2. On CAIMS verify if there are no other associated faults or non communicating LRUs. The ARINC 429 bus from the APU GCU also sends other Generator and GCU faults to DAU 4. You can use System Diagnostics to view each channel of the APU FADEC (APU Oil Temp.) and also access ground faults. Use ATA 31 to see raw data going into the DAU 4, from the APU GCU.

   1. If the APU Generator had not been worked, go to step 4.
   2. If the APU Generator had been worked on in the last 10 hours of APU operation, continue with next step.

3. Remove APU Generator and visually inspect oil passages for blockage, correct orientation of adaptor plate, correct installation and damage.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

4. Verify that the APU air intake inlet door opens fully per AMM TASK 49-14-01-710-801. (DO NOT START THE APU, put the APU control panel knob in the run position only and verify door position visually and on APU DATA status page).

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

5. Inspect the air inlet duct and oil cooler for FOD or signs of blockage or damage. A boroscope type tool can be helpful and prevent timely removals.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

6. Measure the generator temperature and cross-check resistance value between pin A and M of the oil temperature sensor at the auxillary connector of the Auxillary Generator (APU) Generator Connector (A110P1). These values can also be checked at the APU GCU if you have access, just add the wire resistance of about 3 ohms, ref. WM/SSM.

   °C	Ohms Resistance
   10	510-532 ohms
   15	519-541 ohms
   20	528-550 ohms
   25	537-559 ohms
   30	546-568 ohms
   35	555-577 ohms
   40	564-586 ohms
   45	573-595 ohms

   1. If temperature is within range, go to step 8.
   2. If temperature is out of range, continue with next step.

7. Replace the APU Generator.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

8. Perform wiring checks between APU GCU and the APU Generator.

   1. If wiring checks are not good, repair defective wiring as required and do close out.
   2. If wiring checks are good, continue with next step.

9. Swap APU GCU with any other known good GCU on the aircraft. The GCU Testing Harness, 24X-21-03 form the GSE manual is helpful, but not required. It will just save you time from physically swapping the GCUs.

   1. If system checks are good, replace the defective GCU and do close out.
   2. If fault remains, continue with next step.

10. Remove APU Generator and visually inspect oil passages for blockage, correct orientation of adaptor plate and damage.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

11. Remove oil filter elements and do the detailed inspection.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

12. Do close out.