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Home >> Hummer >> 2008 >> H3 Base, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 168 (Cellular System, Entertainment System, And Navigation System) >> Diagnostic Information and Procedures >> OnStar Microphone Inoperative - Caller Cannot Be Heard >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the inside rearview mirror harness connector.
  2. Ignition ON, test for 8.5-9.5 volts between the cellular microphone signal circuit terminal 10 and ground.
    • If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the VCIM.
    • If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the VCIM.
  3. Ignition ON, test for 8.5-9.5 volts between the cellular microphone signal circuit terminal 10 and the drain wire circuit terminal 2.
    • If less than the specified range, test the drain wire circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the VCIM.
  4. If all circuits test normal, replace the inside rearview mirror.
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