Fault Message:

SHORT - EGT SENSOR/CIRCUIT 1 WIRING

Fault Code:

4960150APU

Associated CAS:

APU FAULT
(Advisory)

The Exhaust Gas Temperature (EGT) Sensor 1 conditioning voltage in the Full Authority Digital Engine Control (FADEC) is out of range (low), but the signal read by the FADEC is in the correct range. This shows a possible short to ground in the EGT Sensor or wiring. This fault is shown when the other EGT Sensor is not failed.

• Exhaust-Gas Temperature (EGT) Sensor (TC1)
• Auxiliary Power Unit (APU) Full-Authority Digital Engine-Controller (FADEC) (A108)
• Associated Wiring

Advisory Wire/Servive Bulletin:

• AW700-49-0538 - Auxiliary Power Unit (APU) Exhaust Gas Temperature (EGT) Sensor
• RE220-49-7558 - AIRBORNE AUXILIARY POWER - GAS TURBINE ENGINE - Removal/Replace EGT Sensor, Part No. WE3876282-1 with Part No. WE3876352-1 and Replace/Rework Wiring Harness, Part No. WB3888400-1 with/to part No. WE3888471-1
• RE220-49-8169 - AIRBORNE AUXILIARY POWER - GAS TURBINE ENGINE - Visual Inspection and Sealant Application Method for the Exhaust Gas Temperature (EGT) Sensor, PN WE3876352-1, -2, on RE220 Auxiliary Power Units (APUs)

Forum Articles/Infoservice/Newsletter:

• SIL-APU-87 - AIRBORNE AUXILIARY POWER - GAS TURBINE ENGINE-RE220GX APU Auto Shutdown in Heavy Rain

If CAS message is not active, verify stored faults on CAIMS.

1. Access CAIMS and using active faults, or stored faults find the fault and verify the CAS message. You can use System Diagnostics to view each channel of the APU FADEC (each EGT sensor) in real time, and also access ground faults.
2. Inspect the wiring and connectors to the EGT sensor 1 for any damage.

   1. If defects are found, repair or replace as required and do close out.
   2. If checks are good, continue with next step

3. Inspect the EGT sensor 1 for condition and perform a resistance check between EGT sensor 1 terminals (post-to-post) as follows:

   From	To	Expected Result	Result
   Alumel	Chromel	maximum 0.5 ohms

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

4. Inspect for RTV sealant per APU Auto Shutdown due to rain RE220-49-8169.

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

5. Perform a measurement of the EGT sensor insulation resistance using a Megohmmeter capable of measuring 1 MegaOhm to 1 GigaOhm. Measure from EGT sensor terminal to the EGT sensor flange that attaches to the APU case. The resistance should measure more than 1 MΩ.

   1. If fault remains, replace the defective or damaged EGT probe. Repair the EGT sensor as per RE220-49-8169 and do close out.
   2. If system checks are good, continue with next step.

6. Re-rack FADEC and verify connector A108BP1-K6 and A108BP1-K5 for damage or FOD. Is the fault still present?

   1. If NO, do close out.
   2. If YES, continue with next step.

7. Perform wiring checks between APU firewall connector (P802) and the EGT sensor 1 terminals as follow:

   From	To	Expected Result	Result
   P802-11	Chromel	<5 ohms
   P802-12	Alumel	<5 ohms
   P802-11	Ground Shell	Open
   P802-12	Ground Shell	Open
   Chromel	Ground Shell	Open
   Alumel	Ground Shell	Open

   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.

8. Perform wiring checks between APU firewall connector (J802) and the APU FADEC connector (A108BP1) as follows:

   From	To	Expected Result	Result
   J802-11	A108BP1-K6	<11 ohms
   J802-12	A108BP1-K5	<11 ohms
   J802-11	Ground Shell	Open
   J802-12	Ground Shell	Open
   A108BP1-K6	Ground Shell	Open
   A108BP1-K5	Ground Shell	Open

   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.

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