Diagnostic Instructions
Circuit/System Description
The vehicle communication interface module (VCIM) receives information from a specific GPS antenna located on the outside of the vehicle. The GPS antenna is connected to the VCIM via a shielded coaxial cable. The antenna cable also provides a path for
DC current for powering the antenna.
Diagnostic Aids
| • | The scan tool GPS Signal parameter will display Yes or No dependant upon whether or not the module sees an increment of the seconds transmitted by GPS signals to the VCIM. 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 GPS 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
Component Connector End Views
Description and Operation
OnStar Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
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 the satellites. It is also necessary to inform the OnStar® Call Center
advisor that this call is for vehicle diagnostic purposes.
- Ignition ON, observe the scan tool GPS Signal parameter for at least 10 seconds. The parameter should display Yes.
| ⇒ | If the indicator does not display Yes, refer to GPS Antenna Malfunction. |
- Contact OnStar and verify the OnStar advisor has received the GPS data.
| ⇒ | If the advisor did not receive the GPS data and the call was a "fail to voice", contact the GM Technical Assistance Center. |
| ⇒ | If the advisor did not receive the GPS data and the call was not a "fail to voice", refer to GPS Antenna Malfunction. |
- Verify with the OnStar 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. |
Circuit/System Testing
- Disconnect the harness connector at the radio antenna.
- Ignition OFF, test for less than 10 ohms between the terminal 4 outer shield and ground.
| ⇒ | If greater than the specified range, test the antenna coax shield for an open/high resistance. If the coax tests normal, replace the VCIM. |
- Ignition ON, test the terminal 4 center terminal for 4.5-5.5 volts.
| ⇒ | If greater than the specified range, test the antenna coax center terminal for a short to voltage. If the coax tests normal, replace the VCIM. |
| ⇒ | If less than the specified range, test the antenna coax center terminal for a short to ground or an open/high resistance. If the coax tests normal, replace the VCIM. |
- If all circuits test normal, replace the antenna.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
