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Home >> GMC >> 2018 >> Acadia Denali, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 328 (Active Noise Cancellation System) >> Diagnostic Information and Procedures >> DTC B1277, B127C, B127D, or B126F: Microphone Input Signal >> Circuit/System Testing

Circuit/System Testing

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  1. Ignition OFF, disconnect the harness connector at the appropriate B77 Radio Volume Compensator Interior Noise Microphone. Ignition ON.
  2. Test for 7.8-8.8 V between the signal circuit terminal 2 and ground.
    • If less than 7.8 V 
    1. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier.
    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 T3 Audio Amplifier.
    • If greater than 8.8 V 
    1. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier. Ignition ON.
    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 T3 Audio Amplifier.
    • If between 7.8-8.8 V 
  3. Test for less than 1 V between the signal circuit terminal 1 and ground.
    • If greater than 1 V 
    1. Ignition OFF, X3 harness connector at the T3 Audio Amplifier. Ignition ON.
    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 T3 Audio Amplifier.
    • If less than 1 V 
  4. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier.
  5. Test for infinite resistance between the B77 Radio Volume Compensator Interior Noise Microphone signal circuit terminal 1 and ground.
    • If less than infinite resistance 

      Repair the short to ground in the circuit

    • 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

    • If less than 2 Ω 
  7. Replace the B77 Radio Volume Compensator Interior Noise Microphone.
  8. Ignition ON
  9. Verify the DTC does NOT set.
    • If the DTC sets 

      Replace the T3 Audio Amplifier

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