The entertainment system is controlled by several modules. The radio (IRC) is the radio head, containing the tape and single-disc compact disc (CD) player. The radio amplifier provides the power to drive several speakers. The antenna module controls the selection of the front and rear windshield antennas, and amplifies the resulting signal (FM mode). The CD player (optional) is controlled by the radio, and sends its output to the radio amplifier. The dash integration module (DIM) controls the function of the steering wheel controls. The radio amplifier also allows cellular telephone (if equipped) audio to be played through the speakers, if desired. These modules are linked in several ways. The radio, radio amplifier, DIM and cellular telephone module exchange operating information via class 2 serial data. The CD player and the radio exchange operating information via a dedicated E and C serial data line. Audio, antenna, interior light level and other signals are transmitted via dedicated circuits.

When the door is opened, one vehicle module, the DIM, is alerted, and sends out a wake-up message via class 2 to the other modules. The radio and radio amplifier respond by turning on some portion of their functionality, regardless of ignition switch state or whether the radio is turned on or off. At some point, the chime function is requested via class 2 serial data line. The radio responds by generating a chime signal, and sending it to the radio amplifier, which amplifies the signal and sends it to the left front speaker. When the radio is turned on, it sends a voltage to the antenna module, allowing the antenna module to turn on. If the radio is in AM mode, the radio antenna input is connected directly to the rear antenna (located in the back glass) only. If FM is selected, an additional enable signal is sent to the antenna module. This signal consists of two components: a DC status signal and the varying signal used by the radio. The antenna module responds by turning on the antenna module internal radio amplifier, and selecting between the front and rear antennas, depending on which is providing better reception. (This selection is determined by the signal strength being reported by the radio.) The signal is then amplified and sent to the radio. The radio amplifier always provides at least 10 dB of signal gain.

The radio uses the antenna input signal to create a stereo audio output signal, which is sent at the user-defined volume level to the radio amplifier. The radio amplifier amplifies the signal and sends it to the appropriate speakers. Tone, balance and fade information is sent by the radio via class 2 serial data line and is received by the radio amplifier. Additional output processing is provided by the noise-canceling microphone. The microphone monitors interior ambient noise, and allows the radio amplifier to modify its output so that an enjoyable signal is always heard.

Some audio functions are available using the steering wheel controls. When a steering wheel control button is pressed, a specific resistance value is noted by the DIM. This results in a generated voltage, unique to the particular button. The DIM alerts the radio that the button has been pressed, and the radio responds, just as if the corresponding radio front panel button had been pressed. The tape player, as well as the in-dash CD player, disable the radio tuner and provide their output to the radio amplifier through the same circuitry as the tuner. The CD player, if equipped, communicates with the radio via a dedicated E and C serial data line. When CD player operation is selected, a message is sent to disable the radio output. The player then sends its output directly to the radio amplifier, using a dedicated radio amplifier input circuit completely independent of the radio input to the radio amplifier. When equipped with a cellular telephone, the radio signal may be muted, allowing the telephone audio signal to be heard through the speakers.

The radio is the radio unit seen in the instrument panel of the vehicle, and contains the tape player and the in-dash CD player. The radio receives inputs from class 2 serial data (power mode, date/time, personalization, chime request, etc.), from the antenna module, and from the interior light dimming circuit. The radio provides output to the radio amplifier (audio, equalization, volume), to the antenna module (power, enable command, signal strength), and to the CD player (operating commands). The radio uses its input information to generate an output signal which is sent to the radio amplifier. The front panel radio controls can be divided into two groups. Volume and equalization information is created when the volume, balance, fade and tone controls are adjusted. This information is sent to the radio amplifier via class 2 message, where the equalization is performed. The other front panel button instructions are processed in the radio itself. (Exception: if equipped with a CD player, operating instructions are transmitted to the CD player, where they are performed.) The scan tool has the capability of monitoring the radio switch states, and displaying them. However, checking for proper switch operation does not guarantee that the function is working properly, but only that it is getting the proper command from the switch.

The tape player is an integral part of the radio, therefore, a tape player fault will usually result in replacement of the radio.

The optional CD player is located in the center console. The CD player receives its operating instructions via E&C data line from the radio. The radio amplifier receives the CD player audio information through two dedicated audio lines, and dedicated radio amplifier input circuitry.

The antenna circuit consists of the antenna input of the radio, the antenna module, the COAX signal line between them, the rear window antenna, the front windshield antenna, and two control lines between the radio and the antenna module. When the radio is on, power is sent to the antenna module from the radio. In AM band, the antenna module connects the rear window antenna directly to the radio. When FM band is selected, a DC enable signal is sent from the radio to the antenna module. Superimposed on this enable signal is the strength of the signal being received by the radio tuner. The antenna module now performs two functions. It switches between the front and rear antennas, monitoring the radio signal strength to assure optimum operation. It also amplifies this optimized signal by 10 dB.

The radio antennas are two metallic traces on the top of the windshield, and the top of the rear window. These traces are subject to damage when handled carelessly. If an antenna is damaged, that is, the metallic trace is cut causing an open circuit, the glass must be replaced.

Audio signals are provided to the radio amplifier through three sets of inputs. The radio generates a chime signal and sends it via the chime data line whenever a chime is commanded via class 2. Radio, tape player and in-dash CD player signals are sent from the radio via a pair of shielded audio lines. Output from the CD player is sent via another pair of shielded audio lines. Accordingly, the radio amplifier has three separate input circuits. The radio amplifier processes these input signals, according to the equalization instructions sent from the radio via class 2, amplifies them, and sends them out to the appropriate speakers.

The (UX8), and (UX9) audio systems each contain eight speakers. In the UX8 system, six speakers are contained in the doors. The front doors each contain a full-range speaker and a tweeter; each rear door contains a full-range speaker. The rear package shelf contains a subwoofer speaker with two voice coils. The left door speakers, and the left subwoofer voice coil, are driven by the left channel audio circuitry. The right door speakers, and the right subwoofer voice coil, are driven by the right channel audio circuitry. The dash-mounted center instrument panel midrange speaker is driven by an output signal synthesized from the right and left signals. The UX9 system is similar, except two of the front door speakers are moved to the sides of the top of the instrument panel, and the subwoofer has only one voice coil. One channel (right or left) consists of low-power amplification in the radio of signals generated in the tuner, tape player, or in-dash CD player circuits. These signals are sent by the radio via E&C serial data line to the radio amplifier. The radio amplifier processes the signal (volume, tone, balance, fade) and provides the final power amplification that drives the speakers. If equipped with a CD player, the CD player circuit contains low power amplification and audio lines, similar to those in the radio. The CD outputs are connected to unique, separate input circuits in the radio amplifier, which process the CD signals in the same way as the radio signals are processed by their circuitry. Both of these sets of low-power circuitry feed one common set of output circuits, which provide power to the speakers.

The UX9 audio systems contain a circuit which senses, and compensates for, ambient noise in the vehicle interior. The circuit consists of a microphone, which is located in the upper center headliner above the windshield, an input circuit in the radio amplifier, and the associated wiring. When noise is detected by the microphone, the radio amplifier increases the audio system volume by a proportional amount. The noise canceling circuit may be shut OFF, by turning the AVC OFF using the front panel level control button.