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
* 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)
* Noise Compensation
* Radio Error Messages
* Theft Deterrent
* OnStar (R)
* Steering Wheel Controls
* Auxiliary Input Jack
* Noise Compensation
Radio Circuit Operation
Radio Power
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.
Antenna System
Backglass Antenna
The AM-FM antenna is on the backglass with the rear window defogger, at the top of the rear window.
Make sure that the inside surface of the rear window is not scratched and that the lines on the glass are not damaged. If the inside surface is damaged, it could interfere with radio reception. Using a razor blade or sharp object to clear or clean the inside rear window may damage the rear window antenna and/or the rear window defogger. Do not apply aftermarket glass tinting with metallic film. The metallic film in some tinting materials will interfere with the incoming radio reception.
Antenna Module
The radio antenna is connected to the antenna module. The antenna module is powered by a battery voltage circuit supplied by the radio. The antenna module boosts the received signal and transmits the signal to the radio via a coaxial cable.
Multi-Band Antenna
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(R) and the XM(TM) Satellite Radio 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.
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 radio communicates with the digital radio receiver (DRR) via serial data. During XM operation the audio signals are sent over the left and right audio signal circuits from the DRR 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. A switched 12-volt 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-volt 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.
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, CD-Rs, and CD-RWs. The CD-R/RWs may contain either standard audio (*.cda) or compressed audio (*.mp3). Customers who record their own music CDs should be aware of the following:
* The files can be recorded on a CD-R/RW disc with a maximum capacity of 700 MB.
* The radio will play only compressed audio files recorded in the *.mp3 format. It also supports playlists that can be made and saved with popular MP3 software (in the *.m3u format). A playlist name must be no more than 32 characters in length. If the name of a playlist is longer than 32 characters, the radio will ignore the playlist.
* The radio will only play audio from a CD-R/RW, it cannot record audio.
* The radio will play a mixed mode CD-R/RW (one recorded with both *.cda and *.mp3 files). If a mixed mode CD is inserted in the radio, the radio will assign the standard CD audio to a directory which is listed as ROM audio directory.
* ID3 tag information is displayed by the radio, if available. The ID3 tag information can either be version 1 or 2. The radio will display the file name, song name, artist name, album name, directory name, and playlist name, etc.
* The radio supports multi-session discs, but only the files from the last session will be played.
* There are a total of 20 directories (folders) allowed on a disc. The file structure can be 0-4 directories deep (a folder within a folder, within a folder, etc.) Anything more than 20 directories will be ignored. Each directory may have up to 99 files contained within it. Files not having the *.mp3 extension will not be played, but still count toward the maximum. Anything more than the first 99 files within a directory will be ignored. A single disc may have up to 254 files and directories. Anything beyond the 254 limit will be ignored.
* MP3 files must be written to a CD-R/RW in one of the following industry-standard formats:
- ISO 9660 Level 1
- ISO 9660 Level 2
- Juliet
- Romeo
If the customer does not follow these guidelines when recording a CD-R/RW, the disc may not play in the MP3 Radio.
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 C1). 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 or limit radio functionality if incorrect vehicle information is received by the radio. The radio disables functionality if the VIN information received by the radio does not match the VIN information that has been learned by the radio. A VIN sequence is the last 6 digits of the VIN. The radio receives this information via serial data. A possible cause of incorrect VIN info could be the radio was originally installed in another vehicle.
The radio has the following theft operating modes as part of the theft deterrent system:
* Normal Mode-A radio has received a VIN sequence. The radio only learns the VIN sequence if the VIN sequence contained all 6 digits. In this mode the radio has full functionality.
* No VIN Mode-A radio that has not received or learned a VIN. In this mode the radio has limited 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).
Using the Auxiliary Input Jack (If equipped)
The radio system may have a 3.5 mm auxiliary input jack located on the faceplate. An external audio device such as an MP3 player, CD changer, laptop computer, cassette tape player, etc. can be connected to the auxiliary input jack for use as another source for audio listening. This is not an audio output; do not plug a headphone set into the front auxiliary input jack.
To use a portable audio player, connect a 3.5 mm (1/8 inch) cable to the radio's front auxiliary input jack. While a device is connected, press the radio CD/AUX button to begin playing audio from the device over the vehicle speakers. If there is a CD in the player, pressing the button once will play the CD, pressing again will switch it to the AUX feature.
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. This replaces the conventional speed/volume compensation (SCV) adjustment, which automatically adjusted the audio system volume according to vehicle speed.