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
* Radio/HVAC Communications
* Radio/HVAC Controls
* Antenna System
* AM/FM Reception
* Digital Radio Receiver
* Speaker Operation
* Audio Amplifier
* Radio Data System (RDS)
* Theft Deterrent
* OnStar (R)
* Steering Wheel Controls (If equipped)
* Auxiliary Audio Input Jack
* USB Port
* Auto Volume Control
Radio Circuit Operation
Radio Power
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. 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 Audio Outputs
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.
Navigation Radio Communications Diagram
1 - Radio/HVAC Controls
2 - Info Display Module
3 - Radio
4 - HVAC Control Module
5 - Data Link Connector
a - GMLAN
b - Local Interconnect Network
c - CAN Graphical Interface
d - Digital Video
e - Touch Screen Serial Data
Info Display Module
The info display module has continuous power and ground. When the radio is on, a discrete 12 V signal is supplied on the remote enable circuit to the color display module. This signal is used to control the power state of the module, which is active when the signal is high and inactive when the signal is low.
The info display module receives digital video data from the radio for on-screen display information through the video signal circuits. The radio communicates with the info display module over the touch screen serial data circuits for touch screen inputs and backlighting dimming level.
The screen displays information for Infotainment and Climate Controls, and other vehicle systems such as Charging, Power Flow, and Energy Information, and Vehicle Personalization.
Radio/HVAC Controls
The radio/HVAC controls are a separate component from the radio. The control assembly contains control knobs, switches, buttons and touch controls for all radio and HVAC functions, configuration and personalization, and other vehicle systems. Refer to the Owners Manual for additional information.
The control assembly communicates radio control inputs directly to the radio with the CAN Graphical Interface (CGI) data circuits. After receiving the message the radio will perform the requested function. Messages communicated between the radio and the radio/HVAC controls include the following:
* Button presses/knob rotations
* Commands for the state of indicators
* Radio control back-lighting
HVAC data for controls and status indicators is communicated between the control assembly and the HVAC control module with a separate 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 using the video data circuits.
Antenna System
Multi-Band Antenna
The multi-band antenna is located on the roof of the vehicle. It is used to receive signals for the AM/FM radio, OnStar(R) cellular, GPS signals and the XM(TM) Satellite Radio Service System. 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.
The antenna assembly contains low noise amplifiers for the AM/FM, XM(TM), and GPS antennas that are powered through the coaxial cable by the component that requires the 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
The XM satellite radio 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 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.
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 current delivered to the speaker is rapidly changing alternating current (A/C). This causes the speaker cone to move in two directions producing sound.
Audio Amplifier
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.
Amplifier Operation
The purpose of an amplifier is to increase the power of a voltage or current signal. 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. The output signal of the 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.
Radio Data System (RDS)
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
* 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.
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.
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 previously 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.
OnStar (R)
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 Audio Input Jack
The infotainment system may have a 3.5 mm (1/8 in.) auxiliary audio input jack located in the center console. 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 3.5 mm (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 3.5 mm 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
The infotainment system may have a USB connector located in the center console. The USB port interfaces directly with the radio via a USB cable. When a device is connected to the USB port, the system detects the device and switches to USB as the audio source. Once connected, the device can be controlled from the radio controls. 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. Refer to the Owners Manual for additional information.
Auto Volume Control
A microphone mounted in the vehicle passenger compartment monitors background noise (such as changing road surfaces, driving speeds or open windows). The radio modifies the system's volume and equalization to minimize the effects of unwanted background noise based on the user setting.
Available selections are: OFF, Low, Medium, or High sensitivity.