Diagnostic Aids

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The customer concern may have been due to a lack of cellular service in a given area. A failure in the National Cellular Network infrastructure at the time of the customers failed connection that has since been repaired may also have been the cause.
If an OnStar® Emergency call is able to successfully connect the vehicle to the OnStar® Call Center when an OnStar® Call Center button press is not, there may be a failure in the ability of the OnStar® system in the vehicle to be recognized by the local cellular carrier.
If the prompt "OnStar® request ended" is heard without depressing the white "Dot" button at the end of the an OnStar® keypress, the OnStar® system at one time has 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.

Unable to Contact OnStar Call Center

Step	Action	Value	Yes	No
Schematic Reference: OnStar Schematics Connector End View Reference: Cellular Communication Connector End Views DEFINITION: When the OnStar® Call Center button is pressed, no connection is made to the OnStar® Call Center.
1	Did you perform the cellular Communication Diagnostic System Check?	-	Go to Step 2	Go to Diagnostic System Check - Cellular Communication
2	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. Press the OnStar® Call Center button. Wait for the system to either connect or end the call. Is a connection made with the OnStar® Call Center?	-	Go to Diagnostic Aids	Go to Step 3
3	Other than the normal progression tones of the system and the prompt "Unable to Contact OnStar®", were any other tones or cellular messages heard?	-	Go to Step 4	Go to Step 5
4	IMPORTANT: Placing an emergency call to the OnStar Call Center should only be made if the diagnosis of the system leads to this step. Immediately after an OnStar® advisor picks up the call, they should be told that this call is for diagnostic purposes only and there is no emergency. Record all messages heard from the OnStar® Call Center button press. Press the OnStar® Emergency button. Does the emergency keypress call make a connection to the OnStar® Call Center within 10 minutes?	-	Have all messages heard during the course of the tests available, use the scan tool to access the STID, ESN and Transceiver I.D. and contact the General Motors Technical Assistance Center	Go to Step 5
5	Inspect the cellular and navigation antenna for exterior damage. Is the antenna assembly damaged?	-	Go to Step 9	Go to Step 6
6	Disconnect the cellular antenna coax from the vehicle communication interface module. Disconnect the cellular antenna coax from the cellular and navigation antenna. Measure the resistance from the center conductor of the coax to the metal outer shield. Does the meter read out of limits?	-	Go to Step 7	Go to Step 8
7	Measure the resistance of the cellular antenna coax center conductor from end to end. Does the resistance measure greater than the specified value?	1 Ω	Go to Step 8	Use the scan tool to access the STID, ESN and Transceiver I.D. and contact the General Motors Technical Assistance Center
8	Replace the cellular antenna coax. Did you complete the replacement?	-	Go to Step 10	-
9	Replace the cellular and navigation antenna assembly. Refer to Antenna Assembly Replacement - Cellular and Navigation . Did you complete the replacement?	-	Go to Step 10	-
10	Operate the system in order to verify the repair. Did you correct the condition?	-	System OK	Go to Step 2