Fault Message:

LANDING GEAR ECU [CH 1]/BUS FAULT

Fault Code:

27660231SX

Associated CAS:

GND LIFT DUMP
(Caution)

GND LIFT DUMP
(Advisory)

SPLRS STAB IN TEST
(Advisory)

There is a failure of the ARINC 429 data transmission to Flight Control Unit (FCU) 1.

• Landing Gear Electronic Control Unit (LGECU) (A52)
• Landing Gear Electronic Control Unit (LGECU) Channel A
• Data Acquisition Unit (DAU) 3 (A30)
• Junction Box (JB5)
• Junction Box (JB5)/PCB1
• Flight Control Unit (FCU) 1 (A65)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

This fault may sometime be cleared by performing the flight control system reset procedure.

The status of the FCU can be found in CAIMS:

1. SYSTEM DIAG
2. 27-00 FLIGHT CONTROLS
3. FLIGHT CONTROL UNIT #1
4. LRU TEST
5. DISPLAY MISC. & SENSORS STATUS
6. Go to page 2 of 3
   

1. If the LGECU Channel A is reporting fault or is in red in CAIMS, start troubleshooting LGECU issue first.
   NOTE: The LGECU has two channels, channel A and channel B. Channel A is also called CH 1 and channel B is also called CH 2 in this procedure.
2. Get access to the DAU 3 Active fault. If a fault, related to the LGECU, is reported, troubleshoot it first.
3. Measure for 4.4 VDC or higher at JB5 test points for ARINC 429 Bus as follows:

   ARINC 429 Bus	For 93 pins Test point Connector (JB5 PCB1 P/N 00514-0104-0003)	JB5	FCU 1	DAU 3	LGECU
   High	TP-63	JB5DP1-11B, JB5DP1-11D and JB5DP1-11F	A65AP1-9D	A30CP1-D3	A52BP1-G4
   Low	TP-64	JB5DP1-11C, JB5DP1-11E and JB5DP1-11G	A65AP1-9C	A30CP1-E3	A52BP1-G5

   ARINC 429 Bus	For 96 pins Test point Connector (JB5 PCB1 P/N 00514-0104-0001)	JB5	FCU 1	DAU 3	LGECU
   High	TP-65	JB5DP1-11B, JB5DP1-11D and JB5DP1-11F	A65AP1-9D	A30CP1-D3	A52BP1-G4
   Low	TP-66	JB5DP1-11C, JB5DP1-11E and JB5DP1-11G	A65AP1-9C	A30CP1-E3	A52BP1-G5

   1. If voltage is not present, go to step 8.
   2. If voltage is present, continue with next step.
      NOTE: The test point’s references inside the junction boxes in the wiring diagram are not accurate. (Reference CMM 24-00-01).
      NOTE: Pin to pin and pin to ground wiring checks can be done through the JB test point. Do not perform an insulation test through the junction box.

4. Measure for 4.4 VDC or higher at FCU 1 for ARINC 429 Bus.

   1. If voltage is present, go to step 10.
   2. If voltage is not present, continue with next step.

5. Perform wiring checks between FCU 1 and JB5 test points.

   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 JB5 Circuit Board 1 (JB5 PCB1).

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

7. Replace JB5.

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

8. Measure for 4.4 VDC or higher at DAU 3 for ARINC 429 Bus.

   1. If voltage is present, go to step 6.
   2. If voltage is not present, continue with next step.

9. Measure for short circuit for shorted to ground, shorted to shield, and shorted between wires of ARINC 429 Bus.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.
      NOTE: Remove DAU 3, LGECU and FCU 1 for this test.

10. Swap FCU 1 with FCU 2.

    1. If system checks are good, replace FCU 1. Reset FCUs latched faults and do close out.
    2. If fault remains, continue with next step.

11. Swap DAU 3 with DAU 4.

    1. If system checks are good, replace DAU 3 and do close out.
    2. If fault remains, continue with next step.

12. Re-rack LGECU.

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

13. Perform wiring checks between LGECU and JB5 test points for ARINC 429 Bus.

    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.

14. Replace LGECU.
15. Do close out.