Radio/Audio System
Radio/Audio System Description and Operation
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 RPO Code List.
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 the radio data system (RDS), an audio amplifier, programmable equalizer (EQ), and digital satellite radio (U2K).
Each item in the list below represents topics covered in detail below.
* Radio Circuit Operation
* Radio Faceplate
* Antenna System
* AM/FM Reception
* Digital Radio Receiver
* Speaker Operation
* Audio Amplifier
* Radio Data System (RDS)
* Radio Data System (RDS) Messages
* MP3/CD Formatting Information for MP3/CD Radios (If equipped)
* Integral Multi Disc CD Changer (IMDX)
* Theft Deterrent
* Radio Error Messages
* OnStar (R)
* Steering Wheel Controls
* Auxiliary Input Jack
* USB Port
* Noise Compensation
* Speed Compensated Volume (SCV)
Radio Circuit Operation
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 (PMM) provides the system power mode to the radio via serial data messages. The PMM determines the system power mode by processing power mode information from ignition switch inputs. Serial data 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.
Radio Faceplate
The Radio Faceplate is a separate component from the radio. The faceplate contains the radio control knobs and buttons for all audio functions. In addition, the HVAC head controls are part of the faceplate. The faceplate communicates with the radio through serial data and directly connects to the radio. When the operator rotates a radio 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. Other messages communicated between the radio and the faceplate includes the following:
* The content for the monochrome display
* Button presses / knob rotations
* Commands for the state of indicators
Antenna System
Important: Radio systems with the antenna(s) in the glass are subject to possible interference when an aftermarket window tint is applied.
Diversity Antenna
The diversity antenna system may use both front and back windows with an integral antenna built between the glass layers of the windshield and as an appliqué to the rear glass. Any damage to the 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 front windshield and receives only FM signals.
The antenna reception signals are sorted out by the radio antenna module. The radio antenna module is enabled when the radio is turned on. When the AM or FM band is selected on the radio, the antenna module connects the rear window antenna directly to the radio. In addition, when the FM band is selected an enable signal is sent to the antenna module. Superimposed on this enable signal is the strength of the signal being received by the radio tuner. 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.
AM/FM Reception
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:
* The power output (wattage) of the broadcasting station
* The location of the vehicle (or receiver) relative to the broadcast tower.
* Obstacles between the tower and the receiver
* Atmospheric conditions
* What band (AM or FM) the station is broadcasting
* Type of antenna and the ground plane
AM Reception
The AM band has a lower frequency range than the FM band. These longer wavelengths:
* Bend around Obstacles
* Follow the curvature of the earth
* May reflect off the ionosphere (skip)
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 miles).
FM Reception
The shorter wavelengths of the higher frequency FM band:
* Reflect off obstacles
* Are absorbed by the ground
* Penetrate the ionosphere
Broadcasts in the FM band are limited to line of sight reception which is typically 40 km (25 miles). 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:
* Height of the broadcast antenna
* Height of the receiving antenna
* Terrain and buildings in the broadcast path
Digital Radio Receiver (if equipped)
XM satellite radio provides digital radio reception. The XM signal is broadcast from two satellites and, where necessary, terrestrial repeaters. The high power satellites allow the antenna to receive the XM signal even when foliage and other partial obstructions block the antennas view of the satellite. Terrestrial repeaters are used in dense urban areas. These repeaters will receive the satellite signal and re-broadcast them at much higher power levels in order to ensure reception in areas with densely packed tall buildings. A service fee is required in order to receive the XM service.
The digital radio receiver (DRR) is internal to the Radio.
Speaker Operation
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 1/2 ignition system voltage. This way, the speaker cone can be moved in either direction.
Audio Amplifier (If equipped)
Amplifier Interface
A fused battery voltage circuit provides the main amplifier power. Serial data 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.
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.
Radio Data System (RDS) (If equipped)
The radio may be equipped with the Radio Data System (RDS). The RDS feature is available only on FM stations that broadcast 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.
* RDS functions will only work with FM broadcast stations that are broadcasting RDS data.
* Not all FM Broadcast stations broadcast RDS data or offer all of the RDS services.
* The information displayed is dependent upon the information broadcast by the particular station. The information may vary greatly between stations.
* 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.
* In some cases, a radio station broadcasting incorrect information may cause the RDS features of the radio to appear to work improperly.
With RDS, the radio can do the following:
* Seek to stations broadcasting the selected type of programming
* Receive announcements concerning local and national emergencies
* Display messages from radio stations
RDS may display text information such as:
* The name of the station.
* The type of program.
* General information such as artist and song title, call in phone numbers, etc.
RDS Messages
* 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.
* 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.
MP3/CD Formatting Information for MP3/CD Radios
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:
* The radio will only play audio from a CD-R/RW, it cannot record audio.
* Standard audio and MP3/WMA files should not be mixed on a disc.
* Song title, artist name, and album can display when files are recorded using ID3 tags version 1 and 2.
* 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.
* The radio supports multi-session discs, but only the files from the last session will be played.
Integral Multi Disc CD Changer (IMDX) (If equipped)
The integral multi disc CD changer has the capability of storing and playing up to six (6) 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 vehicle on a normal road with a known good CD. If the condition is still present, 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 ICDX 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.
Theft Deterrent
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 GMLAN frame form.
The radio provides the following theft operating modes as part of the radio theft deterrent system:
* No VIN Mode - A radio that has not received or learned a VIN. In this mode the radio has limited functionality.
* Normal Mode - A radio has received a VIN sequence. The radio only learns the VIN sequence if the VIN sequence contained all six digits. In this mode the radio has full functionality.
* 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.
Radio Error Messages
The Radio may display the following Error Messages (Not all messages may be applicable):
* ERR: This message is displayed when the radio is unable to play the inserted cassette or CD
* LOC: This message is displayed when the radio has entered Theft mode.
* CAL/CAL ERR: This message is displayed when the radio has detected an invalid calibration.
* CDX ERR: Displays if communication is lost with the remote CD changer.
* CHECK CD: Displays when the player encounters a focus or tracking error.
* CHK CDXX: Displays when the CD changer encounters a focus or tracking error.
* CHK TAPE: Displays if a tape has been inserted but is unable to be played due to an error.
* DOOR OPEN: Displays when the CD changer door has been left open.
* NO DISC: Displays when the radio expected a disc to be inserted.
* NONE: Displays when the radio is unable to detect the vehicle speed data information via the serial data circuit.
If an error message is displayed, perform the appropriate diagnostics.
OnStar (R) (if equipped)
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.
For additional OnStar information, refer to OnStar Description and Operation OnStar.
Steering Wheel Controls (if equipped)
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 Steering Wheel Controls.
Auxiliary Input Jack (if equipped)
A remote 3.5mm auxiliary stereo jack and USB connector allows playback of audio signals from remote devices (e.g., laptop computer, iPod, MP3 player, etc.). The remote Aux jack/USB adapter is located in the center console bin. The radio detects the presence or absence of an audio mini-plug through the AuxJackDetect input. When the audio mini-plug is inserted in the Aux Detect Switch the mechanical switch closes. When removed the switch is open.
This is not an audio output; do not plug a headphone set into the front auxiliary input jack.
USB Port (if equipped)
The USB connector uses the USB standards, 1.1 and 2.0. This type of connector supports rates for low speed (1.5 Mb/s), full speed (12 Mb/s), and high speed (480 Mb/s).
USB Supported Devices:
* USB Flash Sticks (Thumb Drives)
* Portable USB Hard Drives
* CompactFlash (or other portable media) adapters
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's display. A special iPod connection cable is needed. This feature supports the following iPod models:
* Fifth generation or later iPod
* First or Second generation or later iPod Nano
For proper operation, make sure the iPod has the latest firmware from Apple(R). The iPod firmware can be updated using the latest iTunes application. See apple.com/itunes. To connect and control the iPod, connect one end of the specially purchased iPod connection cable to the iPod's dock connector. Connect the other end to both the USB port and the auxiliary input jack. The USB port and the auxiliary input jack are located in the center console bin. If the vehicle is on and the USB connection works, a GM logo appears on the iPod. The iPod music displays on the radio's display and begins playing through the vehicle's radio system. A standard iPod USB cable, like the one that came with the iPod, cannot be used to connect an iPod to the vehicle. The iPod connection cable that was purchased with the vehicle or that was made available from the dealer must be used in order for this feature to work.
Noise Compensation (If equipped)
A microphone mounted in the vehicle passenger compartment monitors background noise (such as wind noise from a window being opened) and digitally modifies the system's volume and equalization to ensure optimal sound and performance.
Speed Compensated Volume (If equipped)
With Speed Compensated Volume (SCV), 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. To use SCV, set the volume at the desired level, and then select either Low, Medium, or High. To turn SCV off, select the Off screen button.