Microphone Inoperative - Caller Cannot Be Heard

Microphone Inoperative - Caller Cannot Be Heard

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview

Circuit/System Description

The vehicle communication interface module (VCIM) is a 3-watt cellular device that allows the user to communicate data and voice signals over the national cellular network. It is powered by a fused, battery positive, voltage circuit connected through the vehicle wiring to the 3-button assembly and the radio, and attached by means of coax cables to the cellular and navigation antennas. Ground for the module is accomplished by means of dedicated circuits that are routed with body wiring systems to chassis ground points. The module houses 2 modems, one to process global positioning system (GPS) data, and the other for cellular information. Satellites orbiting earth are constantly transmitting signals of their current location, from which the OnStar(R) system is able to pinpoint its own location. The navigation antenna receives these GPS signals and provides the data to the VCIM to be processed. The VCIM communicates with the rest of the vehicle over the class 2 or GMLAN serial data bus, depending upon the serial data architecture of the vehicle. The ignition state is determined by the VCIM through class 2 or GMLAN messaging. The module also has the capability of commanding the horn, initiating door lock/unlock and operating the exterior lamps using the serial data circuits. When an OnStar(R) keypress is made, a serial data message is sent to the audio system to mute all radio functions and transmit OnStar(R) originated audio. After the audio system is muted, the OnStar(R) signals are transmitted to the audio system on the cellular telephone voice signal circuit, and returned to the module on the cellular telephone voice low reference circuit. The cellular modem connects the OnStar(R) system to the cellular carriers communication system by interacting with the national cellular infrastructure. The module sends and receives all cellular communications over the cellular antenna and cellular antenna coax.

Circuit/System Verification

Important: Perform this diagnostic if the OnStar(R) Call Center operator can clearly be heard but the operator is unable to hear the caller.

1. Ignition ON, press OnStar(R) Call button. Verify that your voice cannot be heard clearly by the OnStar(R) Call Center.

• If your voice can be heard clearly, go to Testing for Intermittent Conditions and Poor Connections in Diagnostic Aids. Component Tests and General Diagnostics

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the cellular microphone.
2. Ignition ON, test for greater than 9 volts between the terminal B and ground.

• If less than specified value, test the cellular microphone signal circuit for an ope/high resistance, for a short to ground, or for a short to the drain wire. If the circuit tests normal, test or replace the VCIM.

3. Test for greater than 9 volts between the terminal B and the terminal A.

• If less than specified value, test the drain wire for an open/high resistance. If the circuit tests normal, test or replace the VCIM.

4. If all circuit test normal, replace the cellular microphone assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

* Control Module References for VCIM replacement, setup, and programming.
* Mobile Telephone Microphone Replacement Verification Tests