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CBV MECHANICALLY FAILED OPEN WITH CLOSED POSITION INDICATION ON EICAS

The Cross Bleed Valve mechanically failed open with a closed position indication on the Engine Indication and Crew Alerting System (EICAS).

• Cross Bleed Valve (L35)
• Junction Box (PCB3/JB4)
• Bleed Management Controller (BMC) 1 (A69)
• Bleed Management Controller (BMC) 2 (A70)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

• When CBV is fully closed, CBV L35P1-5 provides a ground signal (CBV L35 pins 6 and 5 are shorted) to BMCs
• When CBV is fully open, CBV L35P1-1 provides a ground signal (CBV L35 pins 6 and 1 are shorted) to BMCs
• CBV L35P1-6 is connected to Ground Stud GS423 to provide the ground signal for fully closed/fully open to BMCs

1. Manually close CBV.

   1. If CBV cannot be closed, go to step 3.
   2. If CBV closed and EICAS show fully closed, continue with next step.

2. Perform a CBV operational test.

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

3. Replace CBV.

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

4. Perform wiring checks between BMC 1, BMC 2, JB4, CBV and GS423.

   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.
      NOTE: Remove all interface components for short test.

5. Replace BMC 1.

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

6. Replace BMC 2.

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

7. Replace Junction Box JB4 (PCB3/JB4).
8. Do close out.