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(WARNING)
RED MESSAGE (CAUTION)
AMBER MESSAGE (ADVISORY)
CYAN MESSAGE (STATUS)
WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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Quick Links

08/28/25

Message Overview:

SCU Fault Code:

'2'

Associated CAS Message:

NWS FAIL
(Caution)

DDG Reference: None
Reporting LRU: Steering Control Unit
System Description: 32-51-00 - Nosewheel Steering Control System
Schematic Diagram: 32-51-00 - Nosewheel Steering Control System
Wiring Diagram: 32-51-01 - Steering Control Unit

Message Description:

An SCU Fault Code '2' on the SCU 7-segment display indicates a problem with the Steering Selector Valve (SSV) solenoid or with the SSV command or monitoring circuit.

NOTE: If SCU Fault Code '7' is flashing with another code, carry out SCU Fault Code '7' troubleshooting before addressing any other fault.

Possible Causes:

  • Steering Selector Valve (SSV) (V7)
  • Steering Control Unit (SCU) (A73)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Full Throttle Blog/Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

Quick Links:

Automatic Download of the Steering Control Unit (SCU) Non-Volatile Memory (NVM) AMM 32-51-01-970-801
Manual Download of the Steering Control Unit (SCU) Non-Volatile Memory (NVM) AMM 32-51-01-970-802
Removal of the Steering Control Unit AMM 32-51-01-000-801
Installation of the Steering Control Unit AMM 32-51-01-400-801
Removal of the Steering Selector Valve AMM 32-51-09-000-801
Installation of the Steering Selector Valve AMM 32-51-09-400-801
Standard Practices - Continuity and Insulation Check SPM 20-12-01-05
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02
Electrical Connectors - Maintenance Practice - ALL SPM 20-20-00-02

Troubleshooting Recommendations:

Fault Isolation Procedure:

  1. Before starting the following Fault Isolation Procedure, make sure the SCU Fault Confirmation Procedure is carried out to ensure the correct fault code is being addressed.
  2. Measure resistance at the SSV (V7) receptacle per the following table:
    NOTE: Coil resistance value changes with part number

    SSV P/N 4200-2 or P/N 4200-3
    FROM TO EXPECTED RESULTS RESULTS
    A B Between 43Ω - 53Ω  Coil
    SSV P/N 4200-11
    FROM TO EXPECTED RESULTS RESULTS
    A B Between 32Ω - 34Ω Coil

    1. If values are not within range, replace SSV.
    2. If values are in range, go to the next step.

  3. Using a 500 VDC insulation resistance tester (Megger), measure the resistance at the SSV connector per the following table:

    FROM TO EXPECTED RESULTS RESULTS
    A Solenoid Case ≥500MΩ
    A C ≥500MΩ
    B Solenoid Case ≥500MΩ

    1. If values are not within range, replace SSV.
    2. If values are in range, go to the next step.

  4. Carry out a continuity check between SSV and SCU per the following table:

    FROM V7P1 (SSV) TO A73P1 (SCU) RESULTS
    Pin A Pin U
    Pin B Pin T

    1. Repair wiring as required.
    2. If No Fault Found, go to the next step.

  5. Replace SCU.
    scusteering_selector_valvenwss_electrical_schematic

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