GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Envoy - 2WD 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 OnStar Symptom Diagnosis

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • 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 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 left audio signal circuit, and the audio common signal 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 or a failure in the National Cellular Network infrastructure that has since been corrected.
    • If the prompt OnStar Request Ended is heard without pressing the white dot button at the end of an OnStar® keypress, the OnStar® system at one time made a successful cellular connection, but was unable to complete the call. If repeated calls are placed with this result, contact the General Motors Technical Assistance Center.
    •  An inaccurate or aged GPS position may have been due to the temporary loss of GPS signal reception by the vehicle in instances, such as driving through tunnels or parking structures which restrict the navigation antenna from a clear view of the satellites in the sky.

Reference Information

Schematic Reference

OnStar Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

OnStar Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Circuit/System Verification

Important: 

   • To successfully diagnose and repair the OnStar® system it is necessary to comprehend its operation. Technicians should read and understand the OnStar Description and Operation before attempting to repair an OnStar® system. This symptom below will enable the user to verify the customer complaint and narrow it to its source. If there is a concern with voice recognition or OnStar® steering wheel control function, technicians should proceed directly to the applicable diagnostic in Symptoms - Cellular Communication .
   • 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 necessary to inform the OnStar® Call Center advisor that this call is for vehicle diagnostic purposes.

  1. Ignition ON, observe that the OnStar® status LED turns green.
    2. ⇒If the LED does not turn green, refer to OnStar Button LED Inoperative .
  2. Radio ON, set the volume to a comfortable level.
  3. Press the OnStar® Call Center button and observe that the OnStar LED blinks.
    4. ⇒If the OnStar® LED does not blink, refer to OnStar One or More Buttons Inoperative .
  4. Listen that the radio muted and the Connecting to OnStar message played through the audio system.
    5. ⇒If the radio did not mute or the Connecting to OnStar message did not play, refer to No (or Noisy) OnStar Audio .
  5. Wait approximately 10 seconds, then end the call by pressing the white dot button and observe the OnStar LED stops blinking.
    6. ⇒If the OnStar® LED continues blinking, refer to OnStar One or More Buttons Inoperative .
  6. Press the OnStar® Call Center button and ensure that a connection was made with OnStar®.
    7. ⇒If the Unable to Contact OnStar® was heard, refer to Unable to Contact OnStar Call Center .
    ⇒If the OnStar® Request Ended was heard, go to Diagnostic Aids.
  7. Ensure that OnStar® Call Center advisor can hear your voice clearly.
    8. ⇒If the advisor cannot hear you clearly, refer to OnStar Microphone Inoperative - Caller Cannot Be Heard .
  8. Ensure that OnStar® Call Center advisor received a data transfer from the vehicle.
  9. Ensure with the OnStar® Call Center advisor the vehicle has been configured.
    10. ⇒If the vehicle has not been configured, refer to Control Module References
  10. Verify with the OnStar® Call Center advisor that the vehicle identification number (VIN) which they have on record matches the actual VIN.
  11. Verify that your position with the OnStar® Call Center advisor is within a reasonable distance from the actual location of the vehicle.
    12. ⇒If not within a reasonable distance, refer to OnStar Global Positioning System (GPS) Data Not Current or Inaccurate .
  12. Verify with the OnStar® Call Center advisor that the GPS position is marked as Current.
    13. ⇒If not current, refer to OnStar Global Positioning System (GPS) Data Not Current or Inaccurate .
  13. Ensure that the customer concern is the inability of the OnStar® Call Center to perform remote functions.
    14. ⇒If the OnStar® Call Center is able to perform remote functions, go to Diagnostic Aids.
  14. Refer to OnStar Call Center Remote Function Requests Inoperative .

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for VCIM replacement, setup, and programming