Fault Message:

APU OIL FILTER IMPENDING BYPASS

Fault Code:

4960252APU

Associated CAS:

APU FAULT
(Advisory)

The Auxiliary Power Unit (APU) Full-Authority Digital Engine-Controller (FADEC) has detected an oil filter impending bypass.

• Auxiliary Power Unit (APU) Full-Authority Digital Engine-Controller (FADEC) (A108)
• Oil Filter Differential Pressure Switch (S2)
• Auxiliary Power Unit (APU) Generator Control Unit (A109)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

If CAS message is not active, verify stored faults on CAIMS, under System Diagnostics, ATA 49 (this will include ground and air faults).

1. Remove APU oil filter, inspect filter and filter bowl.
2. Perform a detailed inspection of the magnetic drain-plug chip-collector.

   1. If you do not find chips on the chip collector, install a new oil filter and do close out.
   2. If the chips found on the chip collector are no worse than Condition A (refer to AMM 49-90-17-220-801), install a new oil filter and do close out.
   3. If the chips found on the chip collector are equal to or worse than Condition D, install a replacement APU and do close out.
   4. If the chips found on the chip collector are worse than Condition A but less than Condition D (refer to AMM 49-90-17-220-801) and continue with next step.

3. Remove, clean and re-install the gearbox inlet screen.
4. Install new oil filter elements and perform the servicing of the APU oil.
5. Operate the APU for 15 minutes and verify on CAIMS for active APU or GENERATOR OIL FILTER FAULTS.

1. If APU OIL FILTER IMPENDING BYPASS and GENERATOR OIL FILTER IMPENDING BYPASS or only the APU OIL FILTER IMPENDING BYPASS are posted immediately stop the APU, remove and install a replacement APU and do close out.
2. If only the GENERATOR OIL FILTER IMPENDING BYPASS is posted, do the SmartFix + troubleshooting task for the generator oil filter and do close out.
3. If no messages are posted, stop the APU after 15 minutes and inspect the chip collector. Do close out.
4. If the chips found on the chip collector are worse than Condition A (refer to AMM 49-90-17-220-801) remove the APU and install a replacement APU and do close out.
5. If the chips found on the chip collector are no worse than Condition A (refer to AMM 49-90-17-220-801), continue with next step.

6. Check the APU oil level and service as required.
7. Inspect all component replaced for evidence of oil leaks, correct any leak found, operate the APU for 15 minutes.

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

8. Re-rack FADEC and verify connector A108AP1-K2 and A108AP1-K3 for damage or FOD.

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

9. Perform wiring checks between APU FADEC and oil filter differential pressure switch (S2P1), check for 28 volts at S2P1-A of connector.

   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.

10. Replace oil filter differential pressure switch.

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

11. Replace APU FADEC.
12. Call Honeywell FSR before changing APU.
13. Close out.