Circuit Operation through Clear Diagnostic Trouble Code Mode If Available)
RADIO/AUDIO SYSTEM DESCRIPTION AND OPERATIONCONTENTS
- Regular Production Options (RPO)
- 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 Stereo
- (U1C) AM/FM Stereo CD
- (US8) AM/FM Stereo, CD, MP3, RDS, EQ
- (US9) AM/FM Stereo, 6-Disc CD, MP3, RDS, EQ
- (UX7) Base Four Speaker
- (U79) Uplevel Four Speaker
- (UZ6) Premium Audio
- (U2K) Digital Radio
Radio Features:
RADIO FEATURES
CD Players Features:
CD PLAYER FEATURES
MP3 Features:
MP3 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 (UZ6 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 (UZ6 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 (UZ6 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 (UZ6 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 Replacement - Digital Radio 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 CD, MP3, or XM Satellite Radio system is also available when equipped with these options. A VFD (vacuum florescent display) provides system feedback to the operator.
The radio processes the AM and FM signals from the antenna system or the information from the CD media, 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 the UM7 and U1C radios when the ignition is off. Pressing the RCL provides momentary backlighting. Time is not displayed on the US8 and US9 radios when the ignition is off. Pressing RCL will temporarily display the time.
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 speakers, mounted in the doors and rear package shelf. The optional speaker system (RPO UZ6) includes an additional speaker mounted in the front driver and passenger door mirror trim panel.
ONSTAR(R)
OnStar(R) equipped (RPO UE1) vehicles use the radio amplifier and speaker system for voice communication from the OnStar(R) operator to the vehicle. Voice communication from the vehicle to the OnStar(R) operator is through the OnStar(R) microphone and module, which is not a part of the radio system.
When OnStar(R) begins operation, the radio volume is set to a preset level, autotone preset for OnStar(R) 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(R) system are connected through the 12-way connector at the back of the radio. Left and right channel OnStar(R) audio, mute control of radio functions by OnStar(R), 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(R) system. Voice communication from the vehicle to the OnStar(R) operator could be possible under this condition. However, the vehicle occupant will not be able to hear the OnStar(R) operator.
For more information regarding radio operation problems, refer to Symptoms - Radio, Stereo and Compact Disc and Diagnostic System Check - Radio/Audio System. For further information regarding OnStar(R) operation, refer to the OnStar(R) system.
Amplifier
Vehicles equipped with premium audio (RPO UZ6) 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 start-up.
The purpose of an 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 of the input signal, as in the case of a subwoofer or a mid-range amplifier.
CUSTOMER TIPS
Radio Reception - FM
Select Stations Within Range: The best FM fidelity will be obtained from stations within a 16-64 km (10-40 mile) range. Noise or distortion may become apparent when attempting to receive stations at distances greater than this range.
Suggestion: Reduce treble response when attempting to receive fringe stations.
Tall Structures: Tall buildings or hills may cause degrading or loss of signal. FM stations tend to travel "line of sight." Buildings or hills can interrupt the FM signal.
Suggestion: Reduce treble response.
Interference from another station: Although receiver circuits are among the most advanced type available, there are instances where a radio station can be interfered with by another station.
Suggestion: Select another station or switch to a cassette or CD.
Radio Reception - AM
Static Interference During Weather Disturbances: AM reception is sensitive to storm disturbances such as lightning.
Suggestion: Reduce treble response or select an FM station for weather related information.
Care of Compact Discs
- Handle compact discs (CDs) carefully. Touch only the outer edges of the CD or the edge of the hole in the center of the CD. Never touch the glossy side of the CD. Fingerprints and scratches will interrupt the "reading" of the information on the disc.
- Store CDs in their protective cases. Store CDs away from sunlight, dirt, dust, and debris.
- Do not attach a label or tape to a CD.
- Always check for scratches and signs of wear on both sides of the CD.
- Never place any marks on the CD with a marker.
- If a CD becomes contaminated, clean it with a clean, damp, soft, lint-free cloth and mild detergent. Wipe the CD in a straight line from the center hole outward. Do not use cleaning solutions which may damage the CD, such as chemically treated cleaning cloths, benzene, or paint thinners.
Compact Discs Not Appropriate To Use
These CD players were designed to be compatible with round digital audio CDs with the "Compact Disc Digital Audio" label. Other CDs may be incompatible, causing a no-play condition, excessive skips, ERR shown on the radio display or a jam in the loading mechanism. Some incompatible CD types are:
- Special-shaped CDs (any that are not round)
- Re-Writeable CDs (CD-RW type are incompatible)
- Recordable CDs (CD-R type are incompatible, except with US8 or US9 radios)
- Library CDs (with thick bar code labels)
- CD with User-applied labels
On Board Diagnostic Mode (U1C Only)
Follow the instructions below to enter and properly utilize the On Board Diagnostics:
To Enter On Board Diagnostic Mode
1. Key ON, engine OFF, radio in AM/FM mode.
2. Press and hold RCL button, preset 1 button, and preset 6 button.
3. While holding these buttons, press the VOL knob.
4. A beep sounds when the radio enters On Board Diagnostic Mode.
Use the Seek button to advance to the desired mode:
- (T-01) Diagnostic Trouble Code Mode (if available)
- (T-02) Test Tone Mode
- (T-03) LCD Display Segment Mode
- (T-04) Key Test Mode (if available)
- (T-05) Antenna Signal Meter Mode (if available)
- (T-06) Clear Diagnostic Trouble Code Mode (if available)
Press the AM/FM button to select the desired mode. Refer to the Diagnostic Mode descriptions.
Press the RCL button to return to OBD menu or press VOL knob to exit OBD Mode.
Diagnostic Trouble Code Mode (If Available)
Diagnostic Trouble Codes:
The diagnostic trouble code mode is available to provide DTCs and the number of times each code has set. Refer to Enter On Board Diagnostic Mode procedure prior to referencing this information.
To use the DTC Mode:
AM/FM CD Radio-Diagnostic trouble code E04 and the number of times it has set will be displayed first. Codes E01 through E03 do not apply to this radio. Use SEEK rocker button to tab through error codes E04, E05, and E06. Press the RCL button to return to the OBD menu. Press VOL knob to exit OBD.
Test Tone Mode
The Test Tone Mode is available to check for proper speaker function. Once Test Tone mode has been selected, a tone alternating between 100 Hz and 3 kHz will automatically begin to sound. Refer to Enter On Board Diagnostic Mode procedure prior to referencing this information.
To use the Test Tone Mode:
- The display with show "1" indicating the left front speaker is selected.
- Use the SEEK rocker button to move between speakers, "2" indicates right front, "3" indicates left rear, and "4" indicates right rear.
- Press RCL button to return to OBD menu.
If no test tone is heard audibly, increase the volume using the VOL knob. If any of the test tones are not heard from one or more speakers, refer to Speakers Inoperative - One or More.
LCD Display Segment Mode
The LCD Display Segment Mode is available to verify that all display segments are operating properly. Refer to Enter On Board Diagnostic Mode procedure prior to referencing this information. If any display segments are not displayed, replace the radio. Press the appropriate button to return to the OBD menu.
AM/FM CD LCD Display Segment
Key Test Mode (If Available)
The Key Test Mode is available to verify that each button will function. Refer to Enter On Board Diagnostic Mode procedure prior to referencing this information. A tone is generated each time a button is pressed, to confirm button operation. If a button is pressed and a tone is not generated, replace the radio.
IMPORTANT: The RCL button and VOL knob will not produce a tone in this test, as performance of their function is known once the On Board Diagnostic Mode and Key Test Mode have been entered. When the key test is complete, press the appropriate button to return to the OBD menu.
Antenna Signal Meter Mode (If Available)
The antenna signal meter mode is available to evaluate signal strength. Refer to Enter On Board Diagnostic Mode procedure prior to referencing this information. Once this mode is entered, the audio of the last tuned station is played while the signal strength is displayed. This function may be useful for performing a side-by-side, vehicle-to-vehicle comparison, for evaluating audio system reception complaints. Press the appropriate button to return to the OBD menu.
Clear Diagnostic Trouble Code Mode (If Available)
The Clear Diagnostic Trouble Code Mode is available to clear the diagnostic trouble code counters. Refer to Enter On Board Diagnostic Mode procedure prior to referencing this information. Once this mode is selected, press and hold RCL for 2 seconds, a tone will be generated and the DTC counters will reset. Press the appropriate button to return to the OBD menu.