Circuit Operation through Component Description
RADIO/AUDIO SYSTEM DESCRIPTION AND OPERATIONCONTENTS
- RPO Options
- Features
- Circuit Description
- Component Description
- Customer Tips
- On Board Diagnostics
- Theft Deterrent Feature
RPO OPTIONS
The entertainment system on this vehicle is configured with either a base or uplevel audio system. Both the base and uplevel audio systems contain a radio, antenna, and speakers.
The following shows the Entertainment RPOs that are available for this vehicle:
(UM7) AM/FM Radio
(U1C) AM/FM CD Radio
(UP0) AM/FM Cassette/CD Radio
(UR9) AM/FM Cassette/6 Disc CD Radio
- (UW5) Base 6 Speaker
- (U67) Premium Audio(Includes amplifier and subwoofer for VUE; or amplifier and subwoofer rear speakers for ION)
RADIO FEATURES
CASSETTE PLAYER FEATURES
CD PLAYER FEATURES
CIRCUIT OPERATION
Radio Power
The main radio power is supplied by the 10A RADIO (BATT1) fuse in the Body Control Module (BCM). Radio switch-on power, 12 volts in ACC, RUN or RAP, is supplied by the 10A RADIO (ACC) in the BCM.
Radio Grounds
The main radio ground provides a ground for the radio circuits. An additional braided ground strap provides a shielding radio case ground to reduce EMI noise. Both grounds are connected together inside the radio.
Radio Speaker Outputs
At zero volume, the plus (+) and minus (-) speaker outputs are both approximately 5-6 volts, measured to vehicle ground. If a plus or minus for any speaker output is shorted to ground or voltage, the radio circuitry will turn off all 4 speaker outputs for component protection. Above zero volume, the plus and minus change to create a voltage difference between each other, to drive the voice coil of the speaker.
Radio Park Lamp Input
The radio park lamp input allows the radio to sense when the vehicle parking lamps are on. When the parking lamps are on, this circuit goes to battery voltage, and the radio display back-lighting switches from full bright to the brightness level determined by the I/P illumination input.
Radio I/P Illumination Input
A pulse width modulated (PWM) voltage for instrument panel (I/P) illumination is provided to the radio I/P illumination input. The Radio uses this input to directly illuminate the radio buttons and adjust the radio display back-lighting when the park lamp input is on.
Amplifier Power
The main amplifier power is provided by the 20A PREM AUDIO fuse in the Under-Hood Fuse Block (UHFB).
Amplifier Radio Speaker Inputs (U67 only)
The radio speaker outputs, at a reduced output level for amplified systems, are the amplifier inputs. The amplifier boosts these inputs and outputs them to the vehicle speakers. Speaker plus and minus circuits from the radio change to create a voltage difference between each other. If one speaker plus or minus is open between the radio and the amplifier, the input to the amplifier is approximately half because only one of the circuits is changing. The speaker for that channel then operates at approximately only half the normal volume.
Amplifier Speaker Outputs (U67 only)
At zero volume, the plus (+) and minus (-) speaker outputs are both approximately 5-6 volts, measured to vehicle ground. If a plus or minus for any speaker output is shorted to ground or voltage, the amplifier circuitry will turn OFF either the front outputs or rear outputs for component protection. Above zero volume, the plus and minus change to create a voltage difference between each other, to drive the voice coil of the speaker.
Amplifier Present (U67 only)
The amplifier grounds this circuit so the radio can detect an amplified speaker system. When this circuit is grounded, the radio sets the internal equalization to match the amplified speaker system and lowers the radio speaker output level for amplifier input use. If an amplifier is being sensed, the radio OBD equalization setting function will show EQ:00.
Amplifier Radio-On (U67 only)
When the radio is ON, this circuit is pulled to 12 volts by the radio. The amplifier switches ON when this circuit is 12 volts and switches OFF when this signal is 0 volts.
Remote Radio Audio Signal Inputs (UE1 only)
Audio output from the OnStar(R) communications module connects to the remote audio signal inputs of the radio. When the cellular telephone mute signal goes to 0 volts, the radio over-rides any other audio signal and uses these inputs as the source for output to the speakers.
Cellular Telephone Mute (UE1 only)
The OnStar(R) communications module uses the cellular telephone mute signal circuit to over-ride the radio for OnStar(R) communication. When cellular telephone mute is not active, this circuit is held at 2 volts by the radio. When the cellular telephone mute signal is pulled to ground, the radio over-rides any other audio signal and uses the remote audio signals as the source for output to the speakers. If the radio was OFF when this circuit is pulled low, the radio will turn ON. Additionally, the radio fades the speakers to full front, adjusts the volume to an initial audible level, and sets an AutoTone designed for optimal use with OnStar(R). When the mute signal is no longer pulled to ground, the radio returns to the mode it was in previously.
COMPONENT DESCRIPTION
Antenna System
The antenna system receives broadcast AM or FM stereo signals from free space and sends the signals to the radio receiver for processing via a coaxial antenna cable. Good antenna grounding is important for good radio reception.
The antenna base and mast should be installed to the torque specifications provided in the Antenna - Removal and Installation procedures.
The antenna mast is a single 1/4 wave design located at the right front fender.
Ground Strap
The braided ground strap, which is connected between the radio case and the instrument panel fuse block (IPFB), is provided to improve reception and deter noise from entering the audio system.
Radio
The operator interfaces with the radio system through the radio display and controls. Through these controls the operator is able to control system power, volume, fade, balance, bass, and treble equalizations. Control on the integrated tape, single CD or 6-disc CD playback systems is also available when equipped with those options. An LCD (liquid crystal display) provides system feedback to the operator.
The radio processes the AM and FM signals from the antenna system of the information from the cassette tape or CD media sections, amplifies that information and sends the output to the speaker system.
The radio is located in the instrument panel center stack area and is fastened to the instrument panel by 2 fasteners. Guide pins are provided to aid in aligning the radio. Electrical connections to the radio are a 24-way connector from the I/P harness, antenna lead connector and braided ground strap. An additional 12-way harness connector is present on OnStar(R) equipped vehicles. Additional service length is provided in the radio harnesses to allow connection prior to radio installation.
Clock time is displayed continuously on all radio models even then the ignition is OFF. Temporary backlighting is provided if the RCL button is pressed with the ignition OFF. Backlighting is ON whenever the ignition is ON and dims with the instrument panel illumination when the vehicle park lamps are ON.
Radio amplifier outputs to the speakers are protected from damage should speaker leads become shorted to ground or shorted to vehicle power. The radio will sense these conditions and shut down the amplifier outputs in a non-destructive manner. After the short condition is removed, the radio will return to normal operation.
Speakers
The speaker system consists of 4 six inch high sensitivity speakers (HSS) and tweeter speaker mounted in the front driver and passenger door mirror trim panel. The premium audio package (RPO U67) uses the UW5 speakers in the doors and adds a subwoofer.
OnStar(R)
OnStar equipped (RPO UE1) vehicles use the radio amplifier and speaker system for voice communication from the OnStar operator to the vehicle. Voice communication from the vehicle to the OnStar operator is through the OnStar microphone and module, which is not a part of the radio system.
When OnStar begins operation, the radio volume is set to a preset level, autotone preset for OnStar becomes active and the fade control is adjusted to the full front speakers. The radio volume control can then be used to adjust the volume to a desired level.
The radio system and OnStar system are connected through the 12-way connector at the back of the radio. Left and right channel OnStar audio, mute control of radio functions by OnStar, and the audio signal ground are the circuits provided in the 12-way connector.
Disconnecting the 12-way connector from the radio will isolate the radio system from the OnStar system. Voice communication from the vehicle to the OnStar operator could be possible under this condition. However, the vehicle occupant will not be able to hear the OnStar operator.
Amplifier
Vehicles equipped with Premium Audio (RPO U67) include an amplifier. The amplifier has low level inputs from the radio for the 4 speaker channels and amplifies the sound. The amplifier receives a radio on signal from the radio. This signal is delayed momentarily at initial key on to prevent any speaker pops during startup.