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Home >> GMC >> 2018 >> Acadia SL >> Repair and Diagnosis >> External Pages >> Different car >> Section 331 (Cellular System, Entertainment System, And Navigation System) >> Diagnostic Information and Procedures >> DTC B1277: Cellular Phone Microphone Circuit (IOB) >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2017 GMC Acadia. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF/vehicle 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/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
    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 A11 Radio.
    • If greater than 11 V 
    1. Ignition OFF/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
    2. Ignition ON/vehicle in Service Mode, 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 A11 Radio.
    • If between 9-11 V 
  3. Test for less than 1 V between the low reference circuit terminal A and ground.
    • If greater than 1 V 
    1. Ignition OFF/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
    2. Ignition ON/vehicle in Service Mode, test for less than 1 V between the low reference circuit and ground.
      • If 1 V or greater, repair the short to voltage in the circuit.
      • If less than 1 V, replace the A11 Radio
    • If less than 1 V 
  4. Test for greater than 9 V between the signal circuit terminal B and the low reference circuit terminal A.
    • If less than 9 V 
    1. Ignition OFF/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
    2. Test for infinite resistance between the low reference 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 A11 Radio.
    • If greater than 9 V 
  5. Test or replace the B24 Cellular Phone Microphone.
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