No (or Noisy) OnStar Audio

No (or Noisy) OnStar Audio

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 provides an overview of each diagnostic category.

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 inside rearview mirror containing the 3-button assembly and the radio. The VCIM receives its cellular signals 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 left audio signal circuit (+) and the audio common signal 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

1. Ignition ON, radio ON, set volume to comfortable level and press OnStar Center Call button.
2. Verify Connecting to OnStar message is heard clearly through the audio system.

^ If OnStar message is not heard, go to Circuit/System Testing.

3. Tune radio to a known good station and verify that audio is heard clearly through all speaker channels.

^ If no, refer to Speaker Malfunction. Speaker Malfunction

4. If the radio is replaced, the new radio must have the setup procedure performed. Refer to Radio Setup. Programming and Relearning

Circuit/System Testing

Important:
* If the audio common circuit is shorted to voltage the VCIM has been damaged and requires replacement.

* If the vehicle is equipped with the On-Star TTY Interface Module (OTIM), disconnect the OTIM components and restore the connections with the VCIM before continuing diagnosis. If the concern is no longer present with OTIM disconnected, Replace the OTIM system.

1. Disconnect connector X2 from the VCIM.
2. Test for high resistance at the left audio signal circuit (+) terminal 1 for an open or for a short to ground or for a short to voltage.
3. Test for a high resistance, or for a short to voltage at the audio common circuit terminal 2 for an open.
4. If the circuits test normal, test or replace the VCIM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Cellular Communications/Digital Radio Antenna Replacement