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 global positioning system (GPS) signal title on the scan tool will display a Yes or No dependant upon whether or not the module sees an increment of the seconds transmitted by GPS signals to the vehicle communication interface module. Upon entering
this screen, the GPS Signal title will automatically display Yes, regardless of the presence of time increment, for at least 2 seconds, while the algorithm in the scan tool determines the status of the clock. If increment is found, Yes is continually
displayed. If the clock remains static, No is displayed. The scan tool looks for increment every second, regardless of current display. |
| • | Inaccurate or aged GPS position concerns which are no longer present may have been due to the temporary loss of GPS signal reception by the vehicle. Conditions such as driving through tunnels or parking structures while making an OnStar® keypress
will restrict the navigation antenna from a clear view of the satellites in the sky and may have caused this temporary data loss. |
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 Global Positioning System (GPS) data can be received from satellites. It is also necessary to inform the
OnStar® Call Center advisor that this call is for vehicle diagnostic purposes.
- With the scan tool, observe the GPS signal status indicator for at least 10 seconds. Verify the indicator displays Yes.
| ⇒ | If the indicator does not display Yes, go to Component Testing. |
- Call and verify the OnStar advisor receive GPS data.
| ⇒ | If the advisor did not receive GPS data and the call was a 'fail to voice', contact the GM Technical Assistance Center. |
| ⇒ | If the advisor did not received GPS data and the call was not a 'fail to voice' , go to Component Testing. |
- Verify with the OnStar Call Center advisor that your actual position is within a reasonable distance from the actual location of the vehicle.
| ⇒ | If your actual position is not within a reasonable distance from the actual location of the vehicle, replace the VCIM. |
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.
- Disconnect the navigation antenna coax cable from the navigation antenna within the wiring harness.
- Disconnect the navigation antenna from the vehicle communication interface module (VCIM).
- Test for infinite resistance between the center conductor of the coax to the metal outer shield.
| ⇒ | If it does not read infinite, replace the navigation antenna coax cable. |
- Test for greater than 1 ohm resistance at the navigation antenna coax center conductor from end to end.
| ⇒ | If less than specified value, replace the navigation antenna assembly. |
| ⇒ | If greater specified value, replace the navigation antenna coax cable. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
