Fault Message:

APU GEN OPEN POR/FEED/GEN FAULT

Fault Code:

2420108LPS

Associated CAS:

APU GEN FAIL
(Advisory)

Auxiliary Power Unit (APU) Generator has tripped off-line or will not come on-line.

• Auxiliary Power Unit (APU) Generator Control Unit (GCU) (A109)
• Auxiliary Power Unit (APU) Generator (A110)
• AC Power Center (ACPC) (A54)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

A GCU patch cable (GSE REF # 24X-24-02) can be used to swap GCUs 1, 4 and 5 into position 2 or 3 (for troubleshooting only).

The GCU NVMs can only be downloaded at position #2 or #3.

1. Swap APU GCU with GCU #2 (physically or using the GCU patch cable). Is the fault still present?

   1. If NO, replace APU GCU and do close out.
   2. If YES, continue with next step.

2. Disconnect connector A109P1 (APU GCU) and A54P4 (ACPC). Do a continuity check as follows:

   From	To	Result
   A109P1-A	Ground
   A109P1-B	Ground
   A109P1-C	Ground

   1. If there is continuity, repair defective wiring as required and do close out.
   2. If there is no continuity, continue with next step.

3. Do a continuity check as follows:

   From	To	Result
   A109P1-A	A54P4-A
   A109P1-B	A54P4-B
   A109P1-C	A54P4-C

   1. If there is no continuity, repair defective wiring as required and do close out.
   2. If there is continuity, continue with next step.

4. Do a continuity check as follows:

   From	To	Result
   APU GEN stud T1	ACPC stud T13
   APU GEN stud T2	ACPC stud T14
   APU GEN stud T3	ACPC stud T15

   1. If there is no continuity, repair defective wiring as required and do close out.
   2. If there is continuity, continue with next step.

5. Disconnect ACPC studs T13, T14 and T15. Do a continuity check as follows:

   From	To	Result
   APU GEN stud T1	Ground
   APU GEN stud T2	Ground
   APU GEN stud T3	Ground

   1. If there is continuity, repair defective wiring as required and do close out.
   2. If there is no continuity, continue with next step.

6. Do a continuity check on the ACPC as follows:

   From	To	Result
   A54J4-A	Ground
   A54J4-B	Ground
   A54J4-C	Ground

   1. If there is continuity, go to step 8.
   2. If there is no continuity, continue with next step.

7. Do a continuity check on the ACPC as follows:

   From	To	Result
   A54J4-A	ACPC stud T13
   A54J4-B	ACPC stud T14
   A54J4-C	ACPC stud T15

   1. If there is continuity, go to step 9.
   2. If there is no continuity, continue with next step.

8. Replace ACPC.

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

9. Replace APU Generator.
10. Do close out.