Message Name:

EGT SENSOR [CIRCUIT 2 VOLTS OUT HI]

Message Code:

4960157APU

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 sensors can be replaced separately and does not require any adjustments or calibration. It is an 'on condition' component requiring no service. You can access CAIMS to view active or stored faults. You can use CAIMS System Diagnostics to view channel 1 and 2 of the APU FADEC (EGT1 and EGT2 sensors) in real time.

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

   1. If EGT 2 sensor is defective or damaged, go to step 7.
   2. If EGT 2 sensor checks are good, 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 checks are good, go to step 4.
   2. If engine branched wiring-harness defects are found, continue with next step.

3. Replace or repair engine branched wiring-harness.

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

4. 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 defects are found, repair defective wiring as required and do close out.
   2. If no defects are found, continue with next step.

5. Perform wiring checks between APU firewall (P802) and the EGT 2 (TC1-2) sensor as follow:

   From	To	Expected Result	Result
   P802-37	Chromel (+)	<6 Ohms
   P802-36	Alumel (-)	<6 Ohms

   1. If wiring defects are found, repair defective wiring as required and do close out.
   2. If no defects are found, continue with next step.

6. 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 defects are found, repair defective wiring as required and do close out.
   2. If no defects are found, continue with next step.

7. Replace EGT 2.

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

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