Radio/Audio System Description and Operation
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Radio/Audio System Description and Operation
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The entertainment system on this vehicle may have several different configurations available to it. To determine the specific configuration of the vehicle, please see the Service Parts ID Label, and refer to
RPO Code List
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The entertainment system on this vehicle is configured with either a base or an uplevel system. The base and uplevel systems each contain a radio, antenna, speakers, and on some systems an audio amplifier. The uplevel system differs from the base system by providing the customer with enhanced audio system features. Some of those features may include more speakers, an audio amplifier, programmable equalizer, and Digital Audio Broadcast.
Each item in the list below represents topics covered in detail below.
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Radio Circuit Operation
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Radio/HVAC Communications
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Digital Audio Broadcast (if equipped)
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Audio Amplifier (if equipped)
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Radio Data System (RDS) (if equipped)
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Radio Data System (RDS) Messages (if equipped)
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MP3/CD Formatting Information for MP3/CD Radios (if equipped)
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Integral Multi Disc CD Changer (if equipped)
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Rear Seat Audio (RSA) (if equipped)
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Universal Handsfree Phone (if equipped)
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Steering Wheel Controls (if equipped)
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Auxiliary Input Jack (if equipped)
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Multimedia Player Interface Module (if equipped)
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Speed Controlled Volume (SCV) (if equipped)
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Radio Power
The radio is supplied power by a fused B+ circuit. The radio does not use a discrete ignition feed circuit for power moding. The power mode master provides the system power mode to the radio via serial data messages. The power mode master determines the system power mode by processing power mode information from ignition switch inputs. Power modes supported by the radio are OFF, ACCESSORY, RUN, and CRANK REQUEST.
Radio Grounds
The vehicle harness provides a ground for the radio circuits. The radio may also be case grounded.
Radio Data Link Communication
The radio communicates with other modules via serial data.
Radio Outputs
At minimum volume, the plus (+) and minus (-) speaker outputs are approximately half battery voltage, measured to vehicle ground. As the volume increases, the plus and minus change to create a voltage difference between each other either driving the voice coil of the speaker, or being fed to an amplifier.
Radio Head Dimming
Dimming and backlighting levels are determined by the serial data messages the radio receives.
The radio/HVAC controls is a separate component from the radio. The radio/HVAC controls contain the radio control knobs and buttons for all audio functions. Additionally the radio/HVAC controls contain the radio information display.
The radio/HVAC controls operate radio functions through serial data messages.
When equipped with the optional navigation radio, the radio/HVAC controls communicate directly to the navigation radio, and the display communicates information through the signal circuits to the navigation radio.
When the operator rotates a radio control knob to change radio stations or increase the volume a message is sent to the radio over serial data. After receiving the message the radio will make the adjustment. Messages communicated between the radio and the radio/HVAC controls and info display include the following:
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Button presses/knob rotations
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Info display module dimming
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Radio/HVAC controls backlighting
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Graphics and text information
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HVAC data for controls and status indicators is communicated between the radio/HVAC controls and the HVAC control module with a separate Local Interconnect Network (LIN) serial data circuit. HVAC status screen information from the HVAC control module is transmitted to the radio on the GMLAN serial data circuit. The radio then displays the desired screen information on the info display.
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Note
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Radio systems with the antenna(s) in the glass are subject to possible interference when an aftermarket window tint is applied.
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Multi-Band Antenna (If equipped)
The multi-band antenna is located on the roof of the vehicle. This type of antenna may be used with the AM/FM radio, but is primarily for OnStar® and the Satellite Radio (XM)™ Service System, if the vehicle has these features. Keep this antenna clear of snow and ice build up for clear reception. If the vehicle has a sunroof, the performance of the system may be affected if the sunroof is open. Loading items onto the roof of the vehicle can interfere with the performance of the system, ensure the multi-band antenna is not obstructed.
Diversity Antenna (If equipped)
The diversity antenna system may use both the back window antenna and an antenna internal to the antenna module. Any damage to the rear antenna requires replacing the glass. This system is designed to deliver the best radio signal reception possible. Two antennas are used to form a diversity system. The primary antenna is part of the rear window and looks similar to the defogger grid. This antenna receives both AM and FM signals. The secondary antenna is part of the antenna module.
The antenna reception signals are sorted out by the radio antenna module. The radio antenna module is enabled when the radio is turned on. Superimposed on the powered antenna coax is the strength of the signal being received by the antenna module. The antenna module switches between the antennas, monitoring the radio signal strength and combines the signals and phase aligns them to create one strong signal.
Fixed Mast Antenna (If equipped)
The fixed mast antenna can withstand most car washes without being damaged. If the mast should ever become slightly bent, straighten it out by hand. If the mast is badly bent, replace it.
Radio Signal
The radio signal is sent from a broadcast station and is then received by an antenna. The strength of the signal received depends on the following:
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The power output (wattage) of the broadcasting station
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The location of the vehicle (or receiver) relative to the broadcast tower.
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Obstacles between the tower and the receiver
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What band (AM or FM) the station is broadcasting
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Type of antenna and the ground plane
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AM Reception
The AM band has a lower frequency range than the FM band. These longer wavelengths:
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Follow the curvature of the earth
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May reflect off the ionosphere (skip)
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The AM frequencies have longer range due to the ground wave. The ground wave follows the curvature of the earth and is effected by its conductivity. Greater conductivity equates to less signal loss thus transmission over water is better than over land. The AM band has a range of 80-320 km (50-200 mi).
FM Reception
The shorter wavelengths of the higher frequency FM band:
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Are absorbed by the ground
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Penetrate the ionosphere
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Broadcasts in the FM band are limited to line of sight reception which is typically 40 km (25 mi). Even when out of a direct line of sight, the signal may be reflected into areas that would be in a shadow otherwise. Factors which affect the line of sight include:
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Height of the broadcast antenna
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Height of the receiving antenna
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Terrain and buildings in the broadcast path
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Digital Audio Broadcast (if equipped)
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The Digital Radio Broadcast is emitted terrestrial repeaters. A service fee may be required in order to receive the Digital Audio Broadcast service.
The Digital Audio Broadcast receiver is external to the Radio.
Speakers turn electrical energy into mechanical energy to move air, using a permanent magnet and an electromagnet. The electromagnet is energized when the radio or amplifier (if equipped) delivers current to the voice coil on the speaker. The voice coil will form a north and south pole that will cause the voice coil and the speaker cone to move in relation to the permanent magnet. The current delivered to the speaker is rapidly changing alternating current (A/C). This causes the speaker cone to move in two directions producing sound. When the speaker is at rest, such as when the volume at a minimum value, the voltage applied to each side of the speaker is half of the ignition system voltage. This way, the speaker cone can be moved in either direction.
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Audio Amplifier (If Equipped)
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Amplifier Interface
A fused battery voltage circuit provides the main amplifier power. A switched 12 V output from the radio is used to control the power state of the amplifier. To respond quickly to audio input and control signals, the amplifier is ON in all vehicle power modes except OFF and CRANK Request. The internal amplifier bridges are fully powered and unmuted when the amplifier receives the switched 12 V input. This type of amplifier does not have serial data communication capability, and can not set DTCs.
Amplifier Operation
The purpose of the amplifier is to increase the power of a voltage or current signal. The output signal of an amplifier may consist of the same frequencies as the input signal or it may consist of only a portion of the frequencies as in the case of a subwoofer or midrange speaker. The radio creates a low level stereo audio output signal, which is sent at the user defined volume level to the audio amplifier. The audio amplifier amplifies the signal and sends it to the appropriate speakers.
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Radio Data System (RDS) (If Equipped)
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The radio may be equipped with RDS (Radio Data System). The RDS function is only available on FM stations transmitting RDS information. This system relies upon receiving specific information from these stations and only works when the information is available. While the radio is tuned to an FM RDS station, the station name or call letters display.
RDS data is carried in what is known as a "subcarrier". A subcarrier is a frequency that the FM broadcaster is authorized to use to send data that is not audible in the main audio program.
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RDS functions will only work with FM broadcast stations that are broadcasting RDS data.
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Not all FM Broadcast stations broadcast RDS data or offer all of the RDS services.
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The information displayed is dependent upon the information broadcast by the particular station. The information may vary greatly between stations.
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RDS functions may not work properly when reception is weak, reception is of poor quality, or RDS is not implemented properly by the FM Broadcaster.
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In some cases, a radio station broadcasting incorrect information may cause the RDS features of the radio to appear to work improperly.
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With RDS, the radio can do the following:
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Seek to stations broadcasting the selected type of programming
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Receive announcements concerning local and national emergencies
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Display messages from radio stations
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RDS may display text information such as:
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The name of the station.
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General information such as artist and song title, call in phone numbers, etc.
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ALERT!: Alert warns of local or national emergencies. When an alert announcement comes on the current radio station, ALERT! displays. You will hear the announcement, even if the volume is low or a CD is playing. If a CD is playing, play stops during the announcement. Alert announcements cannot be turned off. ALERT! is not affected by tests of the emergency broadcast system. This feature is not supported by all RDS stations.
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INFO (Information): If the current station has a message, the information symbol or INFO displays. Press this button to see the message. The message can display the artist, song title, call in phone numbers, etc. If the entire message can not be displayed, parts of the message appear every three seconds. To scroll through the message, press and release the INFO button. A new group of words displays after every press of this button. Once the complete message has displayed, the information symbol or INFO disappears from the display until another new message is received. The last message is displayed by pressing the INFO button. View the last message until a new message is received or you tune to a different station.
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MP3/CD Formatting Information for MP3/CD Radios
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The MP3/CD equipped radios will play standard audio CDs, and MP3/WMA files that were recorded on a CD-R or CD-RW disc. Customers who record their own music CDs should be aware of the following:
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The radio will only play audio from a CD-R/RW, it cannot record audio.
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Standard audio and MP3/WMA files should not be mixed on a disc.
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Song title, artist name, and album can display when files are recorded using ID3 tags version 1 and 2.
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Long file, folder, or playlist names, or a combination of a large number of files and folders, or playlists can cause the player to be unable to play up to the maximum number of files, folders, playlists, or sessions.
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The radio supports multi-session discs, but only the files from the last session will be played.
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Integral Multi Disc CD Changer (If Equipped)
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The integral multi disc CD changer has the capability of storing and playing up to six compact discs. The integral multi disc CD changer has a shock absorbing system. Only under extreme operating temperatures or severe shock or vibration should the compact disc player skip or mute. If the customer travels an abnormally rough road, a skip condition may be normal. Test drive the car on a normal road with a good CD disc. If the problem remains, replace the radio. The use of CD lens cleaner discs is not advised, due to the risk of contaminating the lens of the CD optics with lubricants internal to the CD mechanism.
The CD mechanism within the radio will begin an initialization routine after a battery connect (e.g., connecting radio connector X1). The initialization process takes approximately 25 seconds to complete. It is very critical that the initialization is completed before removing battery power from the radio, in order for the complex moving parts of the CD mechanism to be positioned properly before shipping and/or handling purposes. Damage may result to the moving parts of the CD mechanism if battery power is removed during the initialization routine. The damage occurs to the CD mechanism during subsequent shipping or handling operations. The extent of the damage causes the CD mechanism not to recover and the mechanism becomes inoperative.
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Rear Seat Audio (RSA) (if equipped)
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The rear seat audio (RSA) feature allows rear seat passengers to listen to a different audio program than the front seat passengers. When RSA is ON, the rear vehicle speakers are muted, and the rear passengers can select their own audio program to listen to using the headphones.
The rear seat passengers can only control the sources that are not being listened by the front seat passengers. For example, rear seat passengers can listen to and control CDs or DVDs through the headphones while the driver listens to the radio through the front speakers. The front seat audio controls always have priority over the RSA controls. If the front seat passengers switch the source for the main radio to a remote source, the RSA is not able to control the source. The rear seat audio can be operated while the main radio is OFF, and the key is RUN, ACCESSORY, or when retained accessory power is active. The rear seat passengers have control of the volume for each set of individual headphones.
Depending on the audio system, the rear speakers may continue to play when the RSA is active through the headphones.
The radio theft deterrent system is intended to disable radio functionality if incorrect vehicle information is received by the radio. The radio disables functionality if the vehicle identification number (VIN) sequence received by the radio (A VIN sequence is usually the last six digits of the VIN.) does not match the VIN information learned by the radio. The radio receives this information in a serial data frame form.
The radio provides the following theft operating modes as part of the radio theft deterrent system:
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No VIN Mode - A radio that has not received or learned a VIN. In this mode the radio has limited functionality.
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Normal Mode - A radio has received a VIN sequence. The radio only adopts the VIN sequence if it contained all six figures. In this mode all radio functions are operative.
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Theft Detected Mode - A radio that had previously learned a VIN sequence and subsequently received a VIN sequence not matching the learned sequence. In this mode the radio has limited functionality.
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The Radio may display the following Error Messages (Not all messages may be applicable):
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ERR: This message is displayed when the radio is unable to play the inserted cassette or CD
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LOC: This message is displayed when the radio has entered Theft mode.
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CAL/CAL ERR: This message is displayed when the radio has detected an invalid calibration.
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CDX ERR: Displays if communication is lost with the remote CD changer.
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CHECK CD: Displays when the player encounters a focus or tracking error.
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CHK CDX: Displays when the CD changer encounters a focus or tracking error.
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DOOR OPEN: Displays when the CD changer door has been left open.
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NO DISC: Displays when the radio expected a disc to be inserted.
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NONE: Displays when the radio is unable to detect the vehicle speed data information via the serial data circuit.
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If an error message is displayed, perform the appropriate diagnostics.
When OnStar is activated, a serial data message is sent to the radio that activates a software program. When the software begins its process, the fade goes to the front, Bass and Treble are set to the mid range, the outputs are mono, and the audio source is OnStar. OnStar takes priority over any other audio source. All of these actions are preset values stored in the radio.
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Universal Handsfree Phone (If Equipped)
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When the universal handsfree phone is activated, a serial data message is sent to the radio that activates a software program. When the software begins its process, the fade goes to the front, Bass and Treble are set to the mid range, the outputs are mono, and the audio source is the universal handsfree phone. The phone takes priority over any other audio source. All of these actions are preset values stored in the radio.
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Steering Wheel Controls (if equipped)
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Some audio functions are available using the steering wheel controls. The steering wheel controls duplicate the function of the primary controls available on the radio.
For additional information on steering wheel controls, refer to
Steering Wheel Controls Description and Operation
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Auxiliary Input Jack (if equipped)
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A remote 3.5 mm auxiliary stereo jack and USB connector allows playback of audio signals from remote devices (e.g., laptop computer, iPod®, MP3 player, etc.). This is not an audio output; do not plug a headphone set into the front auxiliary input jack.
The USB connector uses the USB standards, 1.1 and 2.0. This type of connector supports rates for low speed (1.5 Mbit/s), full speed (12 Mbit/s), and high speed (480 Mbit/s).
USB Supported Devices:
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USB Flash Sticks (Thumb Drives)
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Portable USB Hard Drives
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CompactFlash (or other portable media) adapters
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Depending on the USB mass storage device, some devices may not be recognized. The HUB device is not supported. An iPod® can be controlled using the radio buttons and knobs and display the iPod® song information on the radio display. A special iPod® connection cable is needed. This feature supports the following iPod® models:
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Fifth generation or later iPod®
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First or Second generation or later iPod® Nano
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For proper operation, make sure the iPod® has the latest firmware from Apple®. The iPod® firmware can be updated using the latest iTunes application. See apple.com/itunes To connect and control the iPod®, connect the iPod® to the USB port. If the vehicle is on and the USB connection is present, a GM logo appears on the iPod®. The iPod® music displays on the radio display and begins playing through the vehicle radio system.
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Multimedia Player Interface Module (If Equipped)
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The vehicle may be equipped with a Multimedia Player Interface Module. This module receives multiple incoming digital media signals (USB, Bluetooth, iPOD®, ZUNE®, etc.), then transforms the signals into audio inputs to the radio.
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Speed Controlled Volume (If Equipped)
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With Speed Controlled Volume, the audio system will adjust automatically to make up for road and wind noise as you drive, by increasing the volume as vehicle speed increases.
