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Home >> GMC >> 2018 >> Terrain SL >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Infotainment >> Cellular System, Entertainment System, And Navigation System - Diagnostic Information And Procedures >> Diagnostic Information And Procedures >> DTC B1277: Microphone 1 Input Signal Circuit (IO5/IO6) >> Circuit/System Testing
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Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the B24 Cellular Phone Microphone. Ignition On/Vehicle in Service Mode.
  2. Test for 9 - 11 V between the signal circuit terminal B and ground.
    • If less than 9 V 
    1. Ignition OFF, disconnect the X1 harness connector at the K74 Human Machine Interface Control Module.
    2. Test for infinite resistance between the signal circuit and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K74 Human Machine Interface Control Module.
    • If greater than 11 V 
    1. Ignition OFF, disconnect the X1 harness connector at the K74 Human Machine Interface Control Module. Ignition On/Vehicle in Service Mode.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K74 Human Machine Interface Control Module.
    • Go to next step: If between 9 - 11 V 
  3. Test for less than 1 V between the signal circuit terminal A and ground.
    • If greater than 1 V 
    1. Ignition OFF, X1 harness connector at the K74 Human Machine Interface Control Module. Ignition On/Vehicle in Service Mode.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage in the circuit.
      • If less than 1 V, replace the K74 Human Machine Interface Control Module.
    • Go to next step: If less than 1 V 
  4. Ignition OFF, disconnect the X1 harness connector at the K74 Human Machine Interface Control Module.
  5. Test for infinite resistance between the B24 Cellular Phone Microphone signal circuit terminal A and ground.
    • If less than infinite resistance 

      Repair the short to ground in the circuit

    • Go to next step: If infinite resistance 
  6. Test for less than 2 Ω in the signal circuit end to end.
    • If 2 Ω or greater 

      Repair the open/high resistance in the circuit

    • Go to next step: If less than 2 Ω 
  7. Replace the B24 Cellular Phone Microphone.
  8. Ignition On/Vehicle in Service Mode.
  9. Verify the DTC does NOT set.
    • If the DTC sets 

      Replace the K74 Human Machine Interface Control Module

    • Go to next step: If the DTC does not set 
  10. All OK.
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