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Home >> Buick >> 2021 >> Enclave Preferred >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Secondary And Configurable Customer Controls >> Diagnostic Information and Procedures >> Drive Mode Switch Malfunction >> Circuit/System Testing
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Circuit/System Testing

  1. Ignition/Vehicle OFF, disconnect the harness connector at the S126 Drive Mode Select Switch.
  2. Verify a test lamp illuminates between terminal 5 and B+.
    • If the test lamp does not illuminate 

      Repair the open or high resistance on circuit 1650 or the ground point for circuit 1650.

    • Go to next step: If the test lamp illuminates 
  3. Ignition ON/Vehicle in service mode, test for 4.8 V - 5.2 V between 5 V reference circuit terminal 9 and ground.
    • If less than 4.8 V 
    1. Test circuit 4109 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found.
    2. Test circuit 4109 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found.
    3. Replace the K20 Engine Control Module.
    • If greater than 5.2 V 
    1. Test circuit 4109 for a short to voltage.
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found.
    2. Replace the K20 Engine Control Module.
    • Go to next step: If between 4.8 V - 5.2 V 
  4. Ignition/vehicle OFF, disconnect the X1 connector at the K20 Engine Control Module.
  5. Test for infinite resistance between signal circuit terminal 66 and ground.
    • If less than infinite resistance 
    1. Test circuit 4108 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found.
    2. Replace the S126 Drive Mode Select Switch.
    • Go to next step: If infinite resistance 
  6. Ignition/Vehicle off, connect the S126 Drive Mode Select Switch.
  7. Press and hold the S126 Drive Mode Select Switch.
  8. Test for less than infinite resistance between signal circuit terminal 66 and ground.
    • If infinite resistance 
    1. Disconnect the harness connector at the S126 Drive Mode Select Switch.
    2. Test signal circuit 4108 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found.
    3. Replace the S126 Drive Mode Select Switch.
    • Go to next step: If less than infinite resistance 
  9. Replace the K20 Engine Control Module.
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