Message Name:

APU GCU LOAD LEVEL/OVERCURRENT

The Full-Authority Digital Engine-Controller (FADEC) received incorrect Auxiliary Power Unit (APU) Generator load level inputs because of one or more of the conditions that follow:

• The APU Generator load level input conditioning voltage in the FADEC is out of range high (this shows the APU Generator load level input value is incorrect)
• A signal from the APU Generator load level input is sent to the FADEC when the APU ready to load is not true (this shows the APU Generator load level input value is incorrect)
• A signal from the APU Generator over current input is sent to the FADEC when the APU ready to load is not true (this shows the APU Generator over current input is incorrect)

• Auxiliary Power Unit (APU) Generator Control Unit (GCU) (A109)
• Full-Authority Digital Engine-Controller (FADEC) (A108)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

1. Examine the engine branched wiring-harness for bare wiring, kinks, worn areas and other damage (Refer WM 49-12).

   1. If there is bare wiring, kinks, worn areas or other damage, replace engine branched wiring-harness and do close out.
   2. If not, continue with next step.

2. Perform wiring checks between AC Wiring Harness (P619) and FADEC (A108BP1).

   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.

3. Perform a continuity check as follows:

   From	To	Result
   P619-79	Ground
   P619-80	Ground
   A108BP1-G10	Ground
   A108BP1-H10	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.

4. Perform wiring checks between AC Wiring Harness (P601) and FADEC (A108BP1).

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

5. Perform a continuity check as follows:

   From	To	Result
   P601-A	Ground
   A108BP1-G5	Ground

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

6. Perform wiring checks between AC Wiring Harness (J619) and AC Wiring Harness (P320).

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

7. Perform a continuity check as follows:

   From	To	Result
   J619-79	Ground
   J619-80	Ground
   P320-118	Ground
   P320-117	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.

8. Perform wiring checks between AC Wiring Harness (J601) and AC Wiring Harness (P325).

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

9. Perform wiring checks between AC Wiring Harness (J320) and APU Generator (A109P2).

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

10. Perform a continuity check as follows:

    From	To	Result
    J320-118	Ground
    J320-117	Ground
    A109P2-64	Ground
    A109P2-66	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.

11. Perform wiring checks between AC Wiring Harness (J325) and APU Generator (A109P2).

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

12. Perform a continuity check as follows:

    From	To	Result
    J325-11	Ground
    A109P2-53	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.

13. Perform a check of the EICAS primary display to find EICAS messages that are related to the APU generator.

    1. If there are EICAS messages that are related to the APU generator, troubleshoot the applicable APU generator fault and do close out.
    2. If there are no EICAS messages, continue with next step.

14. Replace FADEC (A108).
15. Do close out.