Radio/Stereo: Description and Operation

AUDIO
An audio system is standard factory-installed equipment on this model, unless the vehicle is ordered with an available radio delete option. The standard equipment audio system includes an AM/FM/cassette (RAS sales code) receiver, and speakers in four locations. Several combinations of radio receivers and speaker systems are offered as optional equipment on this model. The RAS radio uses an ignition switched source of battery current so that the system will only operate when the ignition switch is in the On or Accessory positions. On all other radios, the audio system receives fused battery current from a fuse in the Junction Block (JB) at all times. The internal circuitry of the radio permits the radio to operate dependent on a fused 12 volt signal from the ignition switch. The audio system includes the following components:
- Antenna
- Clockspring (with remote radio switches only)
- High-line Central Timer Module (CTM) (with remote radio switches)
- Power amplifier (with premium speaker system only)
- Radio noise suppression components
- Radio receiver
- Remote radio switches (optional)
- Speakers

(Refer to RESTRAINTS/CLOCKSPRING - DESCRIPTION). (Refer to ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODUL - DESCRIPTION). Following are general descriptions of the remaining major components in the standard and optional factory-installed audio systems.

See the owner's manual for more information on the features, use and operation of each of the available audio systems.

CENTRAL TIMER MODULE
The high-line Central Timer Module (CTM) can also control some features of the audio system when the vehicle is equipped with the optional remote radio switches. A high-line CTM is used on high-line versions of this vehicle. The CTM combines the functions of a chime/buzzer module, an intermittent wipe module, an illuminated entry module, a remote key- less entry module, and a vehicle theft security system module in a single unit.

The high-line CTM also controls and integrates many of the additional electronic functions and features included on models with this option. The RAZ radio receiver with a remote radio switch option is one of the features that the CTM controls. The CTM is programmed to send switch status messages over the Programmable Communications Interface (PCI) data bus to control the volume, seek, and pre-set station advance functions of the optional radio receiver. The CTM monitors the status of the remote radio switches located on the steering wheel through a hard wired circuit. The CTM then sends the proper switch status messages to the radio receiver. The electronic circuitry within the radio receiver responds to the switch status messages it receives by adjusting the radio settings as requested.

(Refer to ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODULE - DESCRIPTION) for more information on the high-line CTM. (Refer to REMOTE SWITCHES DESCRIPTION) for more information on this component. In addition, radio receivers connected to the PCI data bus have several audio system functions that can be diagnosed using a DRB scan tool. Refer to the proper Diagnostic Procedures manual for more information on DRB III testing of the audio systems.

AMPLIFIER (PREMIUM SYSTEM)
Models equipped with the Infinity premium speaker package have a separate power amplifier unit. This power amplifier is a four channel unit. The power amplifier unit is mounted to the right cowl side inner panel under the passenger side end of the instrument panel. The power amplifier unit can be accessed for service by removing the trim from the right cowl side inner panel.

The power amplifier receives fused battery current from a fuse in the Junction Block (JB) at all times. The internal circuitry of the power amplifier switches the amplifier on based upon a fused 12 volt output signal that is received from the radio receiver whenever the radio is turned ON. The power amplifier receives the sound signal inputs for four speaker channels from the radio receiver, then sends the amplified speaker outputs for each of those channels to the six speakers. The Amplifier uses a microprocessor for audio Digital Signal Processing (DSP) and system diagnostics. DSP provides a more accurate and consistent match of the audio system equalization to the vehicle interior, for superior sound quality. This design allows one part number to be used for several vehicles. The amplifier reads the VIN from the Programmable Communications Interface (PCI) data bus.

The Premium Audio Amplifier uses a microprocessor for audio Digital Signal Processing (DSP) and system diagnostics. DSP provides a more accurate and consistent match of the audio system equalization to the vehicle interior. The O2 AN/AN84 Dakota amplifier has four channels for superior sound quality.

The amplifier reads the VIN from the PCI bus and sets itself to match the vehicle. The amplifier will send four beeps to the vehicle speakers at ignition ON, if it does not read the VIN correctly. A replacement amplifier may beep at the first power up, but if these beeps are heard after the first ignition ON, the DRB III should be used to verify the amplifier is connected to the PCI bus and that the VIN on the PCI bus is correct.

The amplifier, wiring to the speakers and the speakers work independently from the radio. The amplifier's microprocessor supports several diagnostic functions. Tests can be run from the DRB III that will help in diagnosing audio system problems. The DRB III can display fault messages when an input or output problem to the amplifier is detected. The amplifier can detect wiring shorts and suggest which wires are likely to be shorted. The amplifier can send test signals that can be used to verify that the amplifier, speakers, and wiring to the speakers are operating properly. The amplifier can also be used to test if the radio is sending audio signals to it. The DRB III can be used to verify the amplifier equalization setting matches the vehicle, in case there is a sound quality complaint. Using the DRB III audio system diagnostics can determine the nature of the problem.

Diagnostic test the Amplifier can perform through the DRB III:
- Continuous Tone Test - This test will send a continuous tone to each speaker and will verify the integrity of an individual channel.
- PCI Amplifier Test - This test will detect a PCI bus or checksum failure.
- Input Test - This test will detect the activity on the amplifiers input channels from the radio.
- Speaker Output Test - This test will detect the activity on the amplifiers output channels to the speakers.

ANTENNA BODY & CABLE
All models use a fixed-length stainless steel rod- type antenna mast, installed on the right front fender of the vehicle. The antenna mast has a spiral groove cut down its length to reduce wind noise. The antenna mast is connected to the center wire of the coaxial antenna cable, and is not grounded to any part of the vehicle. To eliminate static, the antenna base must have a good ground. The coaxial antenna cable shield (the outer wire mesh of the cable) is grounded to the antenna base and the radio receiver chassis.

The antenna coaxial cable has an additional disconnect, located near the outboard side of the glove box opening on the back side of the lower instrument panel reinforcement. This additional disconnect allows the instrument panel assembly to be removed and installed without removing the radio receiver.

RADIO
Available factory-installed radio receivers for this model include an AM/FM/cassette (RAS sales code), an AM/FM/cassette with CD changer controls (RBB sales code), an AM/FM/CD (RBK sales code) or an AM/FM/CD/cassette (RAZ sales code). The factory-in- stalled RBB, RBK and RAZ sales code radio receivers can also communicate on the Programmable Communications Interface (PCI) data bus network through a separate two-way wire harness connector. All factory- installed receivers are stereo Electronically Tuned Radios (ETR) and include an electronic digital clock function.

These radio receivers can only be serviced by an authorized radio repair station. See the latest Warranty Policies and Procedures manual for a current listing of authorized radio repair stations.

The RAS radio receiver operates on fused battery current that is available only when the ignition switch is in the On or Accessory positions. In all radios, the electronic digital clock function of the radio operates on fused battery current supplied through the Ignition Off Draw (IOD) fuse, regardless of the ignition switch position. The RBB, RBK and RAZ radios operate on battery current through the IOD fuse.

The factory installed radio receiver communicates on the Programmable Communication Interface (PCI) data bus network. This is used for the remote radio switches that are mounted to the steering wheel, and also used for radio diagnosis with the DRB III.

The remote radio switches are resistor multiplexed units that are hard wired to the CTM through the clockspring. The CTM monitors the status of the remote radio switches and sends the proper switch status messages on the PCI data bus network to the radio receiver. The electronic circuitry within the radio is programmed to respond to these remote radio switch status messages by adjusting the radio settings as requested.

When troubleshooting output shorts or "output" error messages, the following applies:
- On radios without an external amplifier, the term "output" refers to the path between the radio and the speaker. This type of circuit can be monitored all the way through the speaker connections by the radio assembly. When the radio displays a shorted output DTC with this type of system, the speaker, radio or wiring could be at fault.
- On radios with an external amplifier, the term "output" refers to the circuit between the radio connector and the amplifier. The radio is capable of monitoring only this portion and can tell nothing about the circuit between the amplifier and the speakers. Consequently, a shorted output DTC on this type of system would only refer to this circuit. A faulty speaker could not cause this DTC.

For more information on the features, setting procedures, and control functions for each of the available factory-installed radio receivers, see the owner's manual.

RADIO NOISE SUPPRESSION GROUND STRAP
Radio Frequency Interference (RFI) and ElectroMagnetic Interference (EMI) noise suppression is accomplished primarily through circuitry internal to the radio receivers. These internal suppression devices are only serviced as part of the radio receiver.

External suppression devices that are used on this vehicle to control RFI or EMI noise include the following:
- Radio antenna base ground
- Radio receiver chassis ground wire or strap
- Engine-to-body ground strap(s)
- Exhaust system-to-body ground strap (4.7 L engines only)
- Resistor-type spark plugs
- Radio suppression-type secondary ignition wiring.

For more information on the spark plugs and secondary ignition components, refer to ELECTRICAL/IGNITION CONTROLS.

REMOTE SWITCHES
A remote radio switch option is available on models equipped with the AM/FM/CD/cassette/3-band graphic equalizer (RAZ sales code) radio receiver and the high-line Central Timer Module (CTM). (Refer to ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODUL- DESCRIPTION) for more information on this component.

Fig.14 Remote Radio Switches:

Two rocker-type switches are mounted in the sides of the rear (instrument panel side) steering wheel trim cover. The switch on the left spoke is the seek switch and has seek up, seek down, and preset station advance functions. The switch on the right spoke is the volume control switch and has volume up, and volume down functions. The switch on the right spoke also includes a "mode" control that allows the driver to sequentially select AM radio, FM radio, cassette player or CD player. The two switches are retained in mounting holes located on each side of the rear steering wheel trim cover by four latches that are integral to the switches.

The remote radio switches share a common steering wheel wire harness with the vehicle speed control switches. The steering wheel wire harness is connected to the instrument panel wire harness through the clockspring. (Refer to CLOCKSPRING - DESCRIPTION) for more information on this component.

The remote radio switches are resistor multiplexed units that are hard wired to the high-line Central Timer Module (CTM) through the clockspring. The CTM monitors the status of the remote radio switches and sends the proper switch status messages on the Programmable Communications Interface (PCI) data bus network to the radio receiver. The electronic circuitry within the radio is programmed to respond to these remote radio switch status messages by adjusting the radio settings as requested.

SPEAKER
Standard
The standard equipment speaker system includes speakers in four locations. One full-range 16.5 centimeter (6.50 inch) diameter speaker is located in each front door. There is also one full-range speaker located in each rear cab side panel, 13.3 centimeter (5.25 inch) diameter units for the standard cab models, and 16.5 centimeter (6.50 inch) diameter units for the club cab models. On quad cab models, the 16.5 centimeter (6.50 inch) diameter full-range speaker units are located in each rear door, instead of in the cab side panel.

Each of the four full-range speakers used in the standard speaker system is driven by the amplifier that is integral to the factory-installed radio receiver.

Premium
The optional premium speaker system features Infinity model speakers in six locations. Each of the standard speakers in the four speaker stereo system are replaced with Infinity model speakers, and an additional 6.9 centimeter (2.75 inch) diameter Infinity dome tweeter is mounted high in the front door trim panels. The premium speaker system also includes an additional Infinity power amplifier. The total available power of the premium speaker system is about 160 watts.

The six Infinity speakers used in the premium speaker system are all driven by the radio receiver through an Infinity power amplifier.