Fault Message:

GCU3 SENSE/GEN3 CONT SW FAULT

Fault Code:

2423254LPS

Associated CAS:

GEN 3 FAIL
(Advisory)

Generator Control Unit (GCU) 3 has detected a fault in the Generator Control Switch (GCS)/wiring or in its internal GCS sensing circuit.

GCU GCS sensing circuit has detected the OFF signal as being the same as the ON signal.

• Generator Control Unit (GCU) 3 (A58)
• Electrical Control Panel (Overhead Panel) (AP3)
• Generator Control Switch (GCS)
• 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 GCU 3 with GCU 2.

   1. If system checks are good, replace GCU 3 and do close out.
   2. If fault remains, continue with next step.

2. On GCU #3, disconnect connector A58P2. On the overhead control panel, disconnect connector AP3P2. Perform open circuit checks between GCU 3 and Electrical Control Panel as follow:

   From	To	Expected Result	Result
   A58P2-21	AP3P2-S	Open
   A58P2-28	AP3P2-T	Open

   1. If an open circuit is detected, repair or replace defective wiring as required and do close out.
   2. If an open circuit is not detected, continue with next step.

3. On connector A58P2, perform short circuit checks between GCU 3 and ground as follow:

   From	To	Expected Result	Result
   A58P2-21	Ground	Short
   A58P2-28	Ground	Short

   1. If a short circuit is detected, repair or replace defective wiring as required and do close out.
   2. If a short circuit is not detected, continue with next step.

4. Perform a continuity check between Electrical Control Panel and ground as follows:

   From	To	Result
   AP3P2-R	GC160

   1. If an open circuit is detected, repair or replace the defective wiring as required and continue with next step.
   2. If a short circuit is detected, go to step 6.

5. Check the integrity of ground stud GC160.

   1. If defective, repair or replace the ground stud and do close out.
   2. If it is not defective, do close out.

6. Inspect the electrical control panel internal wiring and the generator control switch (GCS-SDS5).

   1. If a defect is found with the wiring, repair or replace the defective wiring as required and do close out.
   2. If a defect is found on the GCS, continue with next step.

7. Replace the GCS.
8. Do close out.