OnStar Global Positioning System (GPS) Data Not Current or Inaccurate

OnStar Global Positioning System (GPS) Data Not Current or Inaccurate

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 integration module (VCIM) contains two 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 housed in the quad band radio antenna receives these GPS signals and provides the data to the VCIM to be processed. The navigation antenna is connected to the vehicle communication interface module (VCIM) via a shielded coaxial cable. The antenna cable also provides a path for DC current for powering the antenna.

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(R) keypress will restrict the navigation antenna from a clear view of the satellites in the sky and may have caused this temporary data loss.

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(R) Call Center advisor that this call is for vehicle diagnostic purposes.

1. Ignition ON, with a scan tool, observe the GPS signal status indicator for at least 10 seconds. The indicator should display Yes.

• If the indicator does not display Yes, refer to Circuit/System Testing.

2. Call 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 Circuit/System Testing.

3. 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.

Circuit/System Testing

Important: The vehicle may be equipped with sectioned coax cable. Test each section and replace only the faulty section, not the entire length or coax.

1. Ignition OFF, disconnect the navigation antenna coaxial cable from the VCIM and the navigation antenna.
2. Test for less than 5 ohms between the two ends of the coax cable center conductor.

• If greater than the specified range, replace the antenna coax cable.

3. Test for less than 5 ohms between the two ends of the coax cable outer shield.

• If greater than the specified range, replace the antenna coax able.

4. Test for infinite resistance between the antenna coax center conductor and the outer shield.

• If less than the specified range, replace the antenna coax cable.

5. If all circuits test normal, replace the navigation antenna.

Repair Instructions

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

* Cellular Communications/Digital Radio Antenna Replacement