Chevrolet Silverado / GMC Sierra. Service manual — part 2248

VCIM is able to identify which button has been pressed.

The OnStar® status LED is located to the right of the emergency button on a mirror-mounted
assembly and to the left of the answer/end call button when the assembly is mounted on the dash
or overhead console. The LED is green when the system is ON and operating normally. When the
status LED is green and flashing, it is an indication that a call is in progress. When the LED is
red, this indicates a system malfunction is present. In the event there is a system malfunction and
the OnStar® system is still able to make a call, the LED will flash red during the call. The
OnStar® LED is controlled by the VCIM over the keypad red LED signal circuit and the keypad
green LED signal circuit.

OnStar® Microphone

The OnStar®, or cellular microphone can be a part of the rearview mirror assembly, or on some
vehicle lines, can be a separate, stand alone unit. In either case, the vehicle communication
interface module (VCIM) supplies voltage to the microphone on the cellular microphone signal
circuit, while voice data from the user is sent back to the VCIM by means of either a cellular
microphone low reference circuit or a drain wire.

Cellular and Navigation Antennas

This vehicle will be equipped with one of the following types of antennas:

Separate, standalone cellular and navigation antennas

A combination cellular and navigation antenna, which brings the functions of both into a
single part

A cellular, navigation, and digital radio antenna, which also incorporates the functionality
of the digital radio receiver satellite and terrestrial antennas (XM)

The cellular antenna is the component that allows the OnStar® system to send and receive data
over airwaves by means of cellular technology. This antenna is connected at the base to a coax
cable that plugs directly into the vehicle communication interface module (VCIM). The
navigation antenna is used to collect the constant signals of the orbiting satellites. Within the
antenna, is housed a low noise amplifier that allows for a more broad and precise reception of this
data. The current global positioning system (GPS) location is collected by the module every time
a keypress is made. The OnStar® Call Center also has the capability of pinging the vehicle during
an OnStar® call, which commands the module to retrieve the latest GPS location and transmit it
to the OnStar® Call Center. A history location of the last recorded position of the vehicle is
stored in the module and marked as aged. In the event the VCP loses, or is removed from power,
this history location is used by the OnStar® Call Center as a default. Actual GPS location may
take up to 10 minutes to register in the event of a loss of power. This antenna requires a clear and

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

unobstructed path to the satellites in the sky. Window tinting on vehicles may interfere with the
GPS sensor functions, depending upon the location of the GPS antenna and the amount of
darkening and/or metallic particles that are embedded in the film of the tinting material.

OnStar® Sleep Cycle

The OnStar® system uses a unique sleep cycle to allow the system to receive cellular calls while
the ignition is in the OFF position. This cycle enables the vehicle communication interface
module (VCIM) to perform remote functions, such as door unlock, as commanded over the air by
the OnStar® Call Center, when requested by the customer, and to continue to maintain an
acceptable level of battery electrical drain.

This Generation version of OnStar® uses 4 states of readiness, depending upon the type of
cellular market the vehicle is in when the ignition is put into the OFF state:

High power

Low power

Sleep

Digital standby

When in an analog cellular market, 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 1 minute and allows incoming cellular calls to be received. After the 1
minute window, the OnStar® system moves to the sleep state. This state will not recognize or
receive incoming cellular calls. At a predetermined time recorded within the VCIM, up to 9
minutes, the system re-enters the low power state to listen for a call from the OnStar® Call
Center for 1 minute. After this interval, the system will again return to the sleep state for 9
minutes. After these 9 minutes, the system will again enter 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 1 minute interval, the system
will go back into the sleep mode for another 9 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.

In a digital cellular service market the high power state is in effect whenever the ignition is in the
ON or RUN position, and also enables the OnStar® system to send and receive cellular calls and
perform all remote functions. The digital standby power state is in effect after the vehicle has

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

been shut off and the RAP has timed out. When in digital standby mode, the OnStar® module is
able to perform all remote functions as commanded by an OnStar® advisor at any time, for a
continuous 8 hours. After 8 hours, the OnStar® module will follow the standard sleep state as
though in an analog cellular market (9 minutes OFF, 1 minute of digital standby, based on the
time of the global positioning system (GPS) signals).

In the event the OnStar® system loses, or is temporarily removed from battery power, the system
will remain in the sleep state while the key in the OFF position. It will not begin to cycle until the
vehicle passes into an open outside area with the ignition ON, where a GPS signal can be
acquired, providing a reference for time. The OnStar® Call Center is able to maintain a record of
exactly what time each vehicle will enter the 1 minute low power state by synchronizing their
clocks with those of the vehicle, based on GPS signals.

Deactivated OnStar® Accounts

In the event a customer has not renewed their OnStar® account after expiration or the account
was never activated, OnStar® will make a discrete cellular call to the vehicle to deactivate the
OnStar® system. Before taking this action, customers are notified that the OnStar® system in
their vehicle will be deactivated unless they elect to renew the account. After the vehicle has been
successfully deactivated, customers will experience the following when attempting to contact
OnStar® from their vehicle:

During an OnStar® Call Center button press, the customer will be connected to a dedicated
sales team who can sell an OnStar® subscription and reactivate the vehicle. Depending on
the type of OnStar® hardware in the vehicle, the customer may first hear a demonstration
message stating there is no current OnStar® subscription for the vehicle, and directing the
customer what to do to activate services.

During an emergency button press, a demo message will be played indicating the service has
been deactivated.

OnStar® personal calling (OPC) will not be available, as this feature requires the customer
to have a current OnStar® account. Attempts to use this feature may result in cellular
connection failure messages and the inability to connect to the number dialed.

It is of particular note, that when an OnStar® system is successfully deactivated, it will NOT
attempt to connect to the OnStar® Call Center in the event of a collision or if the vehicle's front
air bags deploy for any other reason.

Certain vehicles that have never had an active OnStar® account, that have been deactivated, may
be unable to establish a connection with the OnStar® Call Center. When normal published
diagnostic procedures do not indicate a possible cause for the no connect concern, the vehicle

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

may have been deactivated. For deactivated vehicles, a no connect response should be considered
normal operation. Further diagnosis and subsequent repair is only necessary should the customer
elect to become an active OnStar® subscriber.

OnStar® Reconfiguration Procedure

Within the vehicle communication interface module (VCIM) are a set of unique numbers that
identify the OnStar® customer and the specific vehicle the module resides in. These numbers, the
station identification number (STID) and the electronic serial number (ESN) are transmitted over
the cellular network when an OnStar® keypress is made and are essential for proper
identification and connection to the OnStar® Call Center. In the event the VCIM requires
replacement, the OnStar® reconfiguration procedure must be performed. This procedure allows
for the new STID and ESN within the replacement module to overwrite the old numbers and
update customer and vehicle information at the OnStar® Call Center. The reconfiguration
process is explained within the VCIM replacement procedure, or the OnStar® Reconfiguration
Procedure found in the diagnostic information and procedures section.

The default language for the new VCIM is English. Refer to the scan tool, to change to French or
Spanish.

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
system (GPS).

The cellular operation of the OnStar® system may be inhibited by factors such as the users range
from an analog or digital 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
module, station identification number (STID) and electronic serial number (ESN), 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 coordinates with cellular carriers to resolve connection issues.

The satellites that orbit earth providing the OnStar® system with GPS data have almost 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,

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado