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Circuit/System Testing

Microphone Malfunction

  1. Ignition OFF/vehicle OFF, disconnect the harness connector at the B24 Cellular Phone Microphone, ignition ON/vehicle in Service Mode.
  2. Test for 8.0-10.5 V between the signal circuit terminal B and ground.
    • If less than 8.0 V 
    1. Ignition OFF/vehicle OFF, disconnect the X2 harness connector at the K73 Telematics Communication 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.
      • Go to next step: 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 vehicle K73 Telematics Communication Interface Control Module.
    • If greater than 10.5 V 
    1. Ignition OFF/vehicle OFF, disconnect the X2 harness connector at the K73 Telematics Communication 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.
      • Go to next step: If less than 1 V, replace the K73 Telematics Communication Interface Control Module.
    • Go to next step: If between 8.0-10.5 V 
  3. Test for less than 1 V between the low signal circuit terminal A and ground.
    • If greater than 1 V 
    1. Ignition OFF/vehicle OFF, disconnect the X2 harness connector at the K73 Telematics Communication 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, repair the K73 Telematics Communication Interface Control Module.
    • Go to next step: If less than 1 V 
  4. Test for greater than 8 V between the signal circuit terminal B and the low signal circuit terminal A.
    • If less than 8 V 
    1. Ignition OFF/vehicle OFF, disconnect the X2 harness connector at the K73 Telematics Communication Interface Control Module.
    2. Test for infinite resistance between the low signal circuit and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the low 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 vehicle K73 Telematics Communication Interface Control Module.
    • Go to next step: If greater than 8 V 
  5. Test or replace the B24 Cellular Phone Microphone.

Cellular Telephone Voice Malfunction

  1. Ignition OFF/vehicle OFF, and vehicle systems OFF, disconnect the X2 harness connector at the K73 Telematics Communication Interface Control Module and 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 each signal circuit listed below and ground:
    • K73 Telematics Communication Interface Control Module signal circuit Terminal 6
    • K73 Telematics Communication Interface Control Module signal circuit Terminal 12
    • If greater than 1 V 

      Repair the short to voltage in the circuit.

    • Go to next step: If less than 1 V 
  3. Ignition OFF/vehicle OFF.
  4. Test for infinite resistance between the between each signal circuit listed below and ground:
    • K73 Telematics Communication Interface Control Module signal circuit Terminal 6
    • K73 Telematics Communication Interface Control Module signal circuit Terminal 12
    • If less than infinite resistance 

      Repair the short to ground on the circuit.

    • Go to next step: If infinite resistance 
  5. Test for less than 2 Ω in between each signal circuit listed below end to end:
    • K73 Telematics Communication Interface Control Module signal circuit Terminal 6
    • K73 Telematics Communication Interface Control Module signal circuit Terminal 12
    • If 2 Ω or greater 

      Repair the open/high resistance in the circuit.

    • Go to next step: If less than 2 Ω 
  6. Replace the K73 Telematics Communication Interface Control Module.
  7. Verify that your voice is heard clearly by the OnStar Call Center after completing a blue button press.
    • If your voice can not be heard clearly 

      Replace the K74 Human Machine Interface Control Module.

    • Go to next step: If your voice can be heard clearly 
  8. All OK.
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