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.
Each item in the list below represents topics covered in detail below.
* Radio Circuit Operation
* Information Display and Controls
* Antenna System
* Radio Reception
* Digital Audio Broadcast (if equipped)
* Speaker Operation
* Audio Amplifier (if equipped)
* Theft Deterrent
* Auxiliary Input Jack
* USB Port (if equipped)
* Multimedia Player Interface Module (if equipped)
* OnStar(R) (If equipped)
* Universal Handsfree Phone (if equipped)
* Steering Wheel Controls (if equipped)
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 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, RAP 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
Note: While operating the power folding top, the audio system will mute momentarily to adjust the equalization settings.
Each of the audio output channel circuits (+) and (-), at the radio have a DC bias voltage that is approximately one half of battery voltage. The audio being played on the system is produced by a varying AC voltage that is centered around the DC bias voltage on the same circuit. The AC voltage is what causes the speaker cone to move and produce sound. The frequency (Hz) of the AC voltage signal is directly related to the frequency of the input (audio source playing) to the audio system. Both the DC bias voltage and the AC voltage signals are needed for the audio system to properly produce sound.
Remote Enable Output
The remote enable circuit is a discrete 12 V signal supplied to infotainment system components when the radio is producing audio, needs the front display on, needs video entertainment system components on, or needs to produce chimes. This signal is used to control the power state of the components. There is no output on radio the remote enable circuit when the vehicle is in the CRANK powermode, this is to minimize current consumption from the attached modules and also to avoid audio pops during crank events.
Information Display and Controls
Radio/HVAC Communications
1 - Radio/HVAC Controls
2 - Radio
3 - HVAC Control Module
4 - Data link Connector
a - GMLAN
b - Local Interconnect Network-HVAC
c - CAN Graphical Interface
The radio/HVAC controls is a separate component from the radio, combined into an assembly. The assembly contains the radio control knobs and buttons for all audio and HVAC functions and the information display. The assembly is supplied battery voltage and ground. The radio uses the wake up circuit to control the power state of the display. The radio controls communicate inputs internally to the display. Display backlighting dimming level, graphical data, and radio control inputs are communicated over the CGI serial data circuits between the display and the radio.
Messages communicated between the radio and the radio/HVAC controls include the following:
* Button presses/knob rotations
* Info display dimming
* Radio/HVAC controls back-lighting
* Graphics and text information
Communications between the HVAC controls and the HVAC control module are on a separate LIN circuit. The HVAC control module communicates status information to the radio via GMLAN for HVAC information display.
Antenna System
Note: Radio systems with the antenna(s) in the glass are subject to possible interference when an aftermarket window tint is applied.
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(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.
Active Antenna (U77)
The active antenna system uses an integral antenna applied as an appliqué to the rear glass. The antenna module receives both AM and FM signals from the rear glass antenna. The antenna is part of the rear window and looks similar to the defogger grid. One antenna receives AM signals while the other antenna receives FM signals. Any damage to the antenna requires replacing the glass.
The radio antenna module is enabled when the radio is turned on. The radio provides battery voltage to the antenna module using the center conductor of the antenna coaxial cable. When a 12 V signal is seen by the module on the center conductor of the antenna coax, both AM and FM signals are amplified.
Spoiler Antenna (UB3)
The radio antenna is integral to the spoiler on the rear decklid. The antenna module on the underside of the spoiler receives both AM and FM signals from the antenna. The radio antenna module is enabled when the radio is turned on. The radio provides battery voltage to the antenna module using the remote enable circuit. When a 12 V signal is seen by the antenna module on the remote enable circuit, both AM and FM signals are amplified.
Radio Reception
AM/FM 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.
* Height of the broadcast antenna
* Height of the receiving antenna
* 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
Digital Radio Receiver (If equipped)
The XM satellite receiver is integrated into the radio. 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.
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:
* Display text information such as: station identification, type of programming, and general information (artist and song title, station messages, call in phone numbers, etc.).
* Seek to stations broadcasting the selected type of programming
* Receive announcements concerning local and national emergencies
* Receive alert warnings 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.
Digital Audio Broadcast (If Equipped)
The Digital Radio Broadcast is emitted from 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.
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.
The base (no amplifier) speaker system on the convertible also includes a self-amplified subwoofer. The subwoofer receives audio input from the rear audio signal circuits. The subwoofer assembly receives power and ground from the vehicle harness. The radio controls the power state of the subwoofer via the remote enable circuit.
Audio Amplifier (If Equipped)
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. Each of the audio output channel circuits (+) and (-), from the amplifier have a DC bias voltage that is approximately one half of battery voltage. The audio being played on the system is produced by a varying AC voltage that is centered around the DC bias voltage on the same circuit. The AC voltage is what causes the speaker cone to move and produce sound. The frequency (Hz) of the AC voltage signal is directly related to the frequency of the input (audio source playing) to the audio system. Both the DC bias voltage and the AC voltage signals are needed for the audio system to properly produce sound.
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. 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: The radio has learned a correct VIN sequence and the VIN information received via serial data matches the learned VIN sequence. In this mode the radio has full functionality.
* No VIN Mode: The radio has not received or learned a correct VIN sequence. In this mode the radio has limited functionality.
* Theft Detected Mode: The radio has learned a correct VIN sequence and the VIN information received via serial data does NOT match the learned VIN sequence. In this mode the radio may be disabled or have limited functionality. The radio display will indicate that theft protection is active.
Auxiliary Audio Input Jack
The infotainment system may have a 3.5mm (1/8 in.) auxiliary audio input jack located in the center console. The auxiliary audio input jack may interface directly with the radio, or be connected to the infotainment system via a Multimedia Player Interface Module. When a portable audio playback device is connected to the auxiliary jack, an internal switch detects the connection and the radio will switch to AUX as the audio source. Audio signals from the device are sent to the radio from the auxiliary jack via the left, right, and common audio signal circuits.
* When a device is first connected to the 3.5mm (1/8 in.) input jack the infotainment system automatically switches to that device. If an auxiliary device has already been connected, press the AUX or CD/AUX button to select the device.
* Playback of an audio device that is connected to the 3.5mm jack can only be controlled using the controls on the device.
* The volume control on the device may need to be adjusted to ensure sufficient playback volume through the infotainment system.
USB Port (If Equipped)
The infotainment system may have a USB connector located in the center console. The USB connector may interface directly with the radio, or be connected to the infotainment system via a Multimedia Player Interface Module. The USB connector supports both USB standards 1.1 and 2.0.
USB Supported Devices:
* USB Flash Sticks (Thumb Drives)
* Portable USB Hard Drives
* Portable Digital Media Players ( iPOD(R), ZUNE(R), etc)
Depending on the USB device, some devices may not be recognized, or some features/functions may not be able to be controlled with the radio controls. USB HUB devices are not supported.
Multimedia Player Interface Module (MPIM) (If Equipped)
The vehicle may be equipped with a Multimedia Player Interface Module. This module can receive signals via the USB connector, the auxiliary audio input jack, or a Bluetooth(R) connection. This module receives the incoming signals , then sends the signals as analog audio inputs to the radio.
To allow the radio controls to be used to control portable media devices (USB, Bluetooth, iPOD(R), ZUNE(R), etc); the MPIM translates the USB signals to GMLAN signals to allow the bi-directional communication between the radio and the device. Depending on the device, some devices may not be recognized, or some features/functions may not be able to be controlled with the radio controls. USB HUB devices are not supported.
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 OnStar Description and Operation.
Universal Handsfree Phone (If Equipped)
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.
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 Steering Wheel Controls Description and Operation.