Fault Message:

APUGCU GLC STATUS/SENSING FAULT

Fault Code:

2420231LPS

Associated CAS:

None

Auxiliary Power Unit Generator Control Unit (APU GCU) has detected a the Generator Line Contactor status/status sensing circuit fault, consequently resulting in the APU Generator tripped off-line or not come on-line.

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

A GCU patch cable (GSE REF # 24X-24-02) can be used to swap GCU 1, GCU 2, GCU 3, GCU 4 and the APU GCU into a different position (for troubleshooting only). You can monitor the GCU faults in CAIMS via the active faults page.

1. Are there any other ACPC related CAIMS fault messages?

   1. If YES, troubleshoot them first.
   2. If NO, continue with next step.

2. 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.

3. Access ACPC Primary assembly. Disconnect APULC Status relay (K28) contact A1.
4. Disconnect APU GCU connector A109P2 and do a continuity check as follows:
   

   From	To	Result
   A109P2-19	Ground

   1. If there is continuity, locate the location of the short circuit to ground. Repair defective wiring or replace ACPC if the short circuit is inside the ACPC and do close out.
   2. If there is no continuity, continue with next step.

5. Do a continuity check between APU GCU and APULC Status relay as follows:
   

   From	To	Result
   A109P2-19	K28-A1

   1. If there is no continuity, repair defective wiring as required or replace ACPC if open circuit is inside ACPC and do close out.
   2. If there is continuity, continue with next step.

6. Replace APULC Status relay K28.

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

7. Replace APULC K1.
8. Do close out.