Message Name:

EGT SENSOR [CIRCUIT 2 XREF FAILURE]

Message Code:

4960153APU

Associated CAS:

APU FAULT
(Advisory)

The Auxiliary Power Unit (APU) Full-Authority Digital Engine-Controller (FADEC) detected a failure in the Exhaust-Gas Temperature (EGT) Sensor circuit 2.

• Exhaust Gas Temperature (EGT) Sensor 2 (TC1-2)
• Auxiliary Power Unit (APU) Full Authority Digital Engine-Controller (FADEC) (A108)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Loss of one EGT sensor will not affect APU operation; however an advisory (Cyan) APU FAULT will be displayed on the EICAS primary page, on ground or in flight. Loss of both EGT will cause an APU SHUTDOWN on ground and an APU FAULT message in flight. EGT sensor can be replaced separately and does not require any adjustments or calibration. It is an 'on condition' component requiring no service.You can access the CAIMS to view the Fault Messages.

1. Perform continuity check at the sensor receptacle as per CMM (continuity more than 20 ohms).

   1. If there is no continuity, go to step 6.
   2. If there is continuity, continue with next step.

2. Examine the engine branched wiring-harness for bare wiring, kinks, worn areas and other damage.

   1. If engine branched wiring-harness is damaged, go to step 7.
   2. If engine branched wiring-harness checks are good, continue with next step.

3. Perform wiring checks between sensors EGT 2 (TC1-2) and APU FADEC on connector (A108BP1) as follow:

   From	To	Result
   Chromel (+)	A108BP1-K7
   Alumel (-)	A108BP1-K8

   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.

4. Perform wiring checks between APU firewall (J802) and the EGT 2 (TC1-2) sensor as follow:

   From	To	Expected Result	Result
   J802-36	Alumel (-)	<6 Ohms
   J802-37	Chromel (+)	<6 Ohms

   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.

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

   From	To	Expected Result	Result
   J802-37	A108BP1-K7	<11 Ohms
   J802-36	A108BP1-K8	<11 Ohms

   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.

6. Replace EGT 2.

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

7. Replace or repair engine branched wiring-harness.

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

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