Diagnostic Instructions
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® 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® keypress is made, a serial data message is sent to the audio system to mute all radio functions and transmit OnStar® originated audio. After the audio system is muted, the OnStar® 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® 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.
Diagnostic Aids
| • | The customer concern may have been due to a lack of cellular service in a given area. A failure in the National Cellular Network infrastructure at the time of the customers failed connection that has since been repaired may also have been the cause. |
| • | If an OnStar® emergency call is able to successfully connect the vehicle to the OnStar® Call Center when an OnStar® Call Center button press is not, there may be a failure in the ability of the OnStar® system in the vehicle to be
recognized by the local cellular carrier. |
| • | If the prompt "OnStar® request ended" is heard, without pressing the white dot button at the end of the OnStar® keypress, the OnStar® system at one time has made a successful cellular connection, but was unable to complete the call. If
repeated calls are placed with this result, contact General Motors Technical Assistance Center. |
Reference Information
Schematic Reference
OnStar Schematics
Connector End View Reference
Entertainment/Communication Connector End Views
Description and Operation
OnStar Description and Operation
Electrical Information Reference
Scan Tool Reference
Scan Tool Data List
Circuit/System Verification
Important:
| • | It is important to have the vehicle in an open outside area where a cellular call can be successfully placed and GPS data can be received from satellites. |
| • | Placing an emergency call to the OnStar® Call Center should only be made if the diagnosis of the system leads to step 3. Immediately after an OnStar® advisor picks up the call, they should be told that this call is for diagnostic purposes
only and there is no emergency. |
- Press the OnStar® Call Center button. Verify a connection is not made with the OnStar® Call Center.
| ⇒ | If a connection is made with the OnStar® Call Center, go to Diagnostic Aids. |
- Listen for other tones or cellular messages rather than the normal progression tones or the Unable to Contact OnStar® prompt.
| ⇒ | If no other tones or cellular messages are heard other than the normal progression tones or the Unable to Contact OnStar® prompt, go to Component Testing. |
- Record all messages heard from the OnStar® Call Center button press.
- Press the OnStar® emergency button. Verify a connection to the OnStar® Call Center is made within 10 minutes.
| ⇒ | If a connection is not made within specified time, go to Component Testing. |
- Hear all messages during the course of the tests available, use the scan tool to access the STID, ESN and Transceiver I.D. and contact the General Motors Technical Assistance Center.
Component Testing
Important: Vehicle may be equipped with sectioned coax. Test each section and replace only the faulty section, not the entire length or coax.
- Verify that there is no exterior damage to the cellular antenna.
| ⇒ | If damaged, test or replace the cellular antenna assembly. |
- Disconnect the cellular antenna coax from the VCIM.
- Disconnect the cellular antenna coax from the cellular antenna.
- Test for infinite resistance between the center conductor of the coax and the outer metal shield.
| ⇒ | If different than specified value, replace the cellular antenna coax. |
- Test for less than 1 ohm resistance at the cellular antenna coax center conductor from end to end.
| ⇒ | If greater than specified value, replace the cellular antenna coax cable. |
- Use the scan tool to access the STID, ESN and Transceiver I.D. and contact the General Motors Technical Assistance Center.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
Radio Antenna Base Replacement
