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Home >> Chevrolet >> 2016 >> Suburban 3500 HD LT >> Repair and Diagnosis >> Transmission >> Transfer Case >> Transfer Case - Mp 3023/3024 (NQH) - Diagnostic Information And Procedures >> Diagnostic Information and Procedures >> DTC P185F or P279A-P279C: Transfer Case Range /Four Wheel Drive (4WD) Neutral Range Performance >> Circuit/System Testing

Circuit/System Testing

  1. Monitor the scan tool parameter:4WD Low Signal - (K20)
  2. Operate the component:S77 Transfer Case Shift Control Switch - 4WD Low
  3. Verify the scan tool parameter:4WD Low Signal =Enabled
    • If the parameter does not display the following:Enabled 

      Test or replace the component: Transfer Case Assembly 

    • If the parameter displays the following:Enabled 
  4. Operate the component:S77 Transfer Case Shift Control Switch - 2WD
  5. Verify the scan tool parameter:4WD Low Signal Disabled
    • If the parameter does not display the following:Disabled 

      Test or replace the component:Transfer Case Assembly

    • If the parameter displays the following: =Disabled 
  6. Program the ECM.
  7. Operate the component:S77 Transfer Case Shift Control Switch - 4WD High/Locked
  8. Operate the vehicle within the Conditions for Running the DTC.
  9. Verify the DTC does not set.
    • If the DTC sets 

      Replace the component:K20 Engine Control Module

    • If the DTC does not set 
  10. Operate the component:S77 Transfer Case Shift Control Switch - 4WD Low
  11. Operate the vehicle within the Conditions for Running the DTC.
  12. Verify the DTC does not set.
    • If the DTC sets 

      Replace the component:K20 Engine Control Module

    • If the DTC does not set 
  13. Operate the component:S77 Transfer Case Shift Control Switch -Neutral
  14. Operate the vehicle within the Conditions for Running the DTC.
  15. Verify the DTC does not set.
    • If the DTC sets 

      Replace the component:K20 Engine Control Module

    • If the DTC does not set 
  16. All OK.
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