Cellular Communication System: Diagnosis Chevrolet Tahoe II

Diagnostic Starting Point - Cellular Communication

Begin the diagnosis of the system by performing the Diagnostic System Check for the system in which the customer concern is apparent. Diagnostic System Check - Cellular Communication will direct you to the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Data List

Scan Tool Data List

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

This vehicle will be equipped with either a stand alone navigation antenna or a combination cellular and navigation antenna. The navigation antenna is connected to the VIU with a RG-174 coax cable. The VIU polls the data from the antenna every 2.5 seconds.

Conditions for Running the DTC

1. The ignition must be in the RUN or ACC position.
2. The system voltage is at least 9.5 volts and no more than 15.5 volts.
3. All the above conditions are present for greater than 2.5 seconds.

Conditions for Setting the DTC

1. The VIU does not detect a navigation signal.
2. All the above conditions are present for greater than 2.5 seconds.

Action Taken When the DTC Sets

1. The OnStar® status LED turns RED.
2. The OnStar® Call Center cannot locate the vehicle.

Conditions for Clearing the DTC

1. The VIU detects the presence of a navigation antenna.
2. A history DTC clears after 50 malfunction free ignition cycles.
3. The VIU receives the clear DTC command from the scan tool.

The OnStar® button assembly consists of three buttons, Call/Answer, OnStar® Call Center and OnStar® Emergency. Ten volts is supplied to the button assembly on the keypad supply voltage circuit. Each of the buttons, when pressed, completes the circuit across a resister allowing a specific voltage to be returned to the VIU on the keypad signal circuit. Depending upon the voltage range returned, the VIU is able to identify which button has been pressed.

1. The ignition must be in the RUN or ACC position.
2. The system voltage is at least 9.5 volts and no more than 15.5 volts.
3. All the above conditions are present for greater than 300 ms.

1. The keypad signal circuit voltage to the VIU is less than 2.8 volts or more than 3.2 volts.
2. All the above conditions are present for greater than 300 ms.

1. The VIU will ignore all inputs from the OnStar® button assembly.
2. No calls can be placed.
3. The OnStar® status LED turns RED.

1. The keypad signal circuit voltage is between 2.8 volts and 3.2 volts.
2. A history DTC clears after 50 malfunction free ignition cycles.
3. The VIU receives the clear DTC command from the scan tool.

The Vehicle Communication Unit (VCU) and the Vehicle Interface Unit (VIU) communicate using the OnStar® Serial Data (-) circuit, OnStar® Serial Data (+) circuit and the OnStar® Serial Data Return circuit. DTC U1500 is set when the VIU detects no communication between the VIU and the VCU.

1. The ignition must be in the RUN or ACC position.
2. The system voltage is at least 9.5 volts and no more than 15.5 volts.
3. All the above conditions are present for greater than 300 ms.

1. The VIU detects an open, short to ground or short to B+ on the serial data return circuit.
2. The VIU detects an open, short to ground or short to B+ on serial data (-) circuit.
3. The VIU detects an open, short to ground or short to B+ on serial data (+) circuit.
4. The VIU detects an open on the battery positive voltage circuit.
5. All the above conditions are present for greater than 300 ms.

1. The VIU does not communicate with the VCU.
2. No calls can be placed.
3. The OnStar® status LED turns RED.

1. The VIU does not detect an open, short to ground or short to B+ on the serial data return circuit.
2. The VIU does not detect an open, short to ground or short to B+ on serial data (-) circuit.
3. The VIU does not detect an open, short to ground or short or B+ on serial data (+) circuit.
4. The VIU does not detect an open on the battery positive voltage circuit.
5. A history DTC clears after 50 malfunction free ignition cycles.
6. The VIU receives the clear DTC command from the scan tool.

Diagnostic Aids

1. 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.
2. 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.
3. 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 GPS antenna from a clear view of the satellites in the sky.

OnStar Symptom Diagnosis

Symptoms - Cellular Communication

1. Perform the «Diagnostic System Check - Cellular Communication»(ref-189228-S28641353172005090700000) before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «OnStar Description and Operation»(ref-189228-S37924554612005090700000) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the system. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-175720-S08180388062005042600000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «OnStar One or More Buttons Inoperative»(ref-189228-S23177476832005090700000)
2. «Unable to Contact OnStar Call Center»(ref-189228-S37209516372005090700000)
3. «OnStar Call Center Unable to Configure OnStar (R) System»(ref-189228-S33932142502005090700000)
4. «OnStar Button LED Inoperative»(ref-189228-S11790003852005090700000)
5. «No (or Noisy) OnStar Audio»(ref-189228-S02916422942005090700000)
6. «Microphone Inoperative - Caller Cannot Be Heard»(ref-189228-S10674584172005090700000)
7. «OnStar Always On»(ref-189228-S00591105952005090700000)
8. «Voice Recognition Inoperative»(ref-189228-S00662533802005090700000)
9. «OnStar Reconfiguration»(ref-189228-S01889989182005090700000)
10. «Global Positioning System (GPS) Data Not Current or Inaccurate»(ref-189228-S10292022302005090700000)
11. «OnStar Call Center Remote Function Requests Inoperative»(ref-189228-S36660065152005090700000)

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.

OnStar Call Center Remote Function Requests Inoperative

1. 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 customer's failed connection that has since been repaired may also have been the cause.
2. 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.
3. 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

1. 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 Interface Unit. Upon entering this screen, the "GPS Signal" title will automatically display "Yes", regardless of the presence of time increment, for at least two 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.
2. Inaccurate or aged GPS position concerns made by a customer 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.

Global Positioning System (GPS) Data Not Current or Inaccurate

OnStar Battery Consumption Test

In order to allow the OnStar® system to receive cellular calls and perform remote functions (such as door unlock) while the ignition is in the OFF position, and maintain an acceptable level of battery drain, the Vehicle Interface Unit uses a unique sleep cycle. In the event the OnStar® system is not cycling properly, excessive current draw from the battery may result. This procedure is designed to determine which one of the two OnStar® control modules is the source of a battery drain once the battery electrical drain test has been performed and it is has been concluded that the OnStar® subsystem is the source of the parasitic load.

The OnStar® system uses three states of readiness

1. High Power
2. Low Power
3. Sleep

The High power state is in effect whenever the ignition is in the "ON" or "RUN" position, and enables the OnStar® system to send and receive cellular calls and perform all remote functions.

The Low power state is entered once the vehicle ignition is placed in the "OFF" position and the Retained Accessory Power (RAP) function has been turned off, or times out. This state will last for one minute after the ignition state reaches the "OFF" position and allows incoming cellular calls to be received. The Low power state will pull approximately 250mA from the battery.

After the one minute "window", the OnStar® system moves to the Sleep state, where the lowest current draw is maintained at approximately .5mA. This state will not recognize or receive incoming cellular calls and will last for nine minutes.

After this nine-minute interval, the system will wake up to the Low state of power and listen for any incoming calls that the OnStar® Call Center may be sending. In the event a call is being sent, the OnStar® system will receive the call and immediately go into the High power mode to perform any requested functions. If no call is received during the one-minute interval, the system will go back into the sleep mode for another nine minutes. This process will continue for up to 48 hours, after which, the OnStar® system will permanently enter the Sleep state until the ignition is once again turned to the "ON" or "RUN" position.

The OnStar® Call Center is able to maintain a record of exactly what time each vehicle will enter the one-minute Low power state by synchronizing their clocks with those of the vehicle, based on GPS signals.

Scheme 42

1. If the vehicle has not been reconfigured correctly or configured at all, the system may not enter and cycle through each of the power states correctly.
2. In the event the OnStar® system loses, or is temporarily removed from battery power, the sleep cycle will not begin until the vehicle passes into an open outside area where a GPS signal can be acquired, providing a reference for time.

OnStar Battery Consumption Test

OnStar® Cellular, GPS, and Diagnostic Limitations

The proper operation of the OnStar® System is dependent on several elements outside the components integrated into the vehicle. These include the National Cellular Network Infrastructure, the cellular telephone carriers within the network, and the Global Positioning Satellite system.

The cellular operation of the OnStar® system may be inhibited by factors such as the user's range from an analog cellular tower, the state of the cellular carriers' equipment, and the location where the call is placed. Making an OnStar® keypress in areas that lack sufficient cellular coverage or have a temporary equipment failure will result in either the inability of a call to complete with a data transfer or the complete inability to connect to the OnStar® Call Center. The OnStar® system may also experience connection issues if the identification numbers for the modules (STID and ESN numbers) are not recognized by the cellular carriers local signal receiving towers. OnStar® cellular connection issues such as these require the assistance of the General Motors Technical Assistance Center OnStar® Group, which coordinate with cellular carriers to resolve connection issues.

The satellites that orbit earth providing the OnStar® system with GPS data have nearly no failures associated with them. In the event of a no GPS concern, the failure will likely lie with the inability of the system to gain GPS signals because of its location (i.e. in a parking structure), hardware failure, or being mistaken with an OnStar® call which has reached the Call Center without vehicle data.

During diagnostic testing of the OnStar® system, the technician should ensure the vehicle is located in an area that has a clear unobstructed view of the open sky, and preferably, an area where analog, cellular calls have been successfully placed. These areas can be found by successfully making an OnStar® keypress in a known good OnStar® equipped vehicle and confirming success with the OnStar® Call Center advisor. Such places can be used as a permanent reference for future OnStar® testing.