OnStar Microphone Inoperative - Caller Cannot Be Heard
OnStar Microphone Inoperative - Caller Cannot Be Heard
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provide an overview of each diagnostic category.
Diagnostic Fault Information
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 voltage circuit connected through the vehicle wiring to the 3-button OnStar(R) assembly located on the inside rearview mirror. The VCIM and radio are attached by means of coax cables to the cellular and navigation antennas. 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 GMLAN serial data bus. 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 GMLAN 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 Testing
1. Ignition OFF, disconnect the harness connector at the cellular microphone.
2. Ignition OFF, test for less than 5 ohms between the drain wire circuit terminal A and ground.
^ If greater 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.
3. Ignition ON, test for 9.5-10.5 volts between the cellular microphone signal circuit terminal B 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.
4. If all circuits test normal, replace the cellular microphone.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Mobile Telephone Microphone Replacement