Message Name:

APU SPEED OUT OF RANGE

The Full-Authority Digital Engine-Controller (FADEC) stopped the Auxiliary Power Unit (APU) or recorded incorrect Speed Sensor inputs because of one or more of the conditions that follow:

• Speed Sensor 1 Built-In Test signal in the FADEC is set true (this shows a possible short or open in the Speed Sensor or Engine Branched Wiring-Harness)
• Speed Sensor 2 Built-In Test signal in the FADEC is set true (this shows a possible short or open in the Speed Sensor or Engine Branched Wiring-Harness)
• The FADEC did not receive correct Speed Sensor 1 and 2 inputs (in this condition, the FADEC will prevent a start or cause an APU shutdown)

• Full-Authority Digital Engine-Controller (FADEC) (A108)
• Speed Sensor (MT4)
• 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 there is no damage, continue with next step.

2. Examine the speed sensor (MT4) receptacle for contamination and damage.

   1. If there is contamination or damage, go to step 8.
   2. If there is no contamination or damage, continue with next step.

3. Perform a resistance check as follows:

   From	To	Expected Result	Result
   MT4-A	MT4-B	54.08-81.12 Ohms

   1. If the resistance value is not as specified, go to step 8.
   2. If the resistance value is as specified, continue with next step.

4. Perform a resistance check as follows:

   From	To	Expected Result	Result
   MT4-D	MT4-E	115.52-173.28 Ohms

   1. If the resistance value is not as specified, go to step 8.
   2. If the resistance value is as specified, continue with next step.

5. Perform wiring checks between APU (P802) and speed sensor (MT4P1).

   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.

6. Perform a continuity check as follows:

   From	To	Result
   J802-13	Ground
   J802-14	Ground
   J802-39	Ground
   J802-40	Ground
   MT4P1-A	Ground
   MT4P1-B	Ground
   MT4P1-D	Ground
   MT4P1-E	Ground

   1. If there is continuity, replace engine branched wiring-harness and do close out.
   2. If there is no continuity, continue with next step.

7. Perform wiring checks between wiring harness (J802AC) and FADEC (A108BP1).

   From	To	Result
   J802-13	A108AP1-G11
   J802-14	A108AP1-H11
   J802-39	A108AP1-J11
   J802-40	A108AP1-K11

   1. If the wiring checks are not good, repair defective wiring as required and do close out.
   2. If the wiring checks are good, replace FADEC (A108) and do close out.

8. Replace the speed sensor (MT4).
9. Do close out.