Diagnostic Instructions
Circuit/System Description
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 housed in the quad band radio antenna receives these GPS signals and provides the data to the vehicle communication integration module VCIM to be processed.
Diagnostic Aids
| • | The 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
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. 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 VCIM navigation antenna coax cable from the radio antenna.
- Disconnect the navigation antenna coax cable from the 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 less than 1 ohm resistance at the navigation antenna coax center conductor from end to end.
| ⇒ | If greater specified value, replace the navigation antenna coax cable. |
| ⇒ | If less than specified value, replace the radio antenna base. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
