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. Several combinations of radio receivers and speaker systems are offered as optional equipment on this model. 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 ELECTRICAL/RESTRAINTS/CLOCKSPRING - DESCRIPTION). (Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODUL - DESCRIPTION). For complete circuit diagrams, refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds. 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 keyless 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 and RBQ 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 ELECTRICAL/ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODUL - DESCRIPTION) for more information on the high-line CTM. (Refer to ELECTRICAL/AUDIO/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 III scan tool.

Refer to the proper Diagnostic Procedures manual for more information on DRB III testing of the audio systems.

AMPLIFIER
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. For complete circuit diagrams, refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.

ANTENNA BODY & CABLE
All models use a fixed-length stainless steel rodtype 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:
- AM/FM/cassette with CD changer control feature (RBB sales code)
- AM/FM/CD/cassette with equalizer (RAZ sales code)
- AM/FM/CD with CD changer control feature (RBK sales code)
- AM/FM/CD with 6 CD changer (RBQ sales code)
- AM/FM/CD/cassette (RBY sales code) - export only

All factory-installed radio receivers can communicate on the Programmable Communications Interface (PCI) data bus network. 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 radios operate on battery current through the Ignition Off Draw (IOD) fuse. The electronic digital clock function of the radio operates on fused battery current supplied through the IOD fuse, regardless of the ignition switch position.

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. For complete circuit diagrams, refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.

RADIO NOISE SUPPRESSION GROUND STRAP
Radio noise suppression devices are factory-installed standard equipment on this vehicle. Radio Frequency Interference (RFI) and ElectroMagnetic Interference (EMI) can be produced by any on-board or external source of electromagnetic energy. These electromagnetic energy sources can radiate electromagnetic signals through the air, or conduct them through the vehicle electrical system.

When the audio system converts RFI or EMI to an audible acoustic wave form, it is referred to as radio noise. This undesirable radio noise is generally manifested in the form of "buzzing," "hissing, popping," "clicking," "crackling," and/or "whirring" sounds. In most cases, RFI and EMI radio noise can be suppressed using a combination of vehicle and component grounding, filtering and shielding techniques. This vehicle is equipped with factory-installed radio noise suppression devices that were designed to minimize exposure to typical sources of RFI and EMI; thereby, minimizing radio noise complaints.

Factory-installed radio noise suppression is accomplished primarily through circuitry or devices that are integral to the factory-installed radios, audio power amplifiers and other on-board electrical components such as generators, wiper motors, blower motors, and fuel pumps that have been found to be potential sources of RFI or EMI. External radio noise suppression devices that are used on this vehicle to control RFI or EMI, and can be serviced, include the following:

Engine-to-body ground strap - This length of braided ground strap has an eyelet terminal connector crimped to each end. One end is secured to the engine cylinder head(s). The other is secured to the plenum.

Resistor-type spark plugs - This type of spark plug has an internal resistor connected in series between the spark plug terminal and the center electrode to help reduce the production of electromagnetic radiation that can result in radio noise.

There are two common strategies that can be used to suppress Radio Frequency Interference (RFI) and ElectroMagnetic Interference (EMI) radio noise. The first suppression strategy involves preventing the production of RFI and EMI electromagnetic signals at their sources. The second suppression strategy involves preventing the reception of RFI and EMI electromagnetic signals by the audio system components.

The use of braided ground straps in key locations is part of the RFI and EMI prevention strategy. These ground straps ensure adequate ground paths, particularly for high current components such as many of those found in the starting, charging, ignition, engine control and transmission control systems. An insufficient ground path for any of these high current components may result in radio noise caused by induced voltages created as the high current seeks alternative ground paths through components or circuits intended for use by, or in close proximity to the audio system components or circuits.

Preventing the reception of RFI and EMI is accomplished by ensuring that the audio system components are correctly installed in the vehicle. Loose, corroded or improperly soldered wire harness connections, improperly routed wiring and inadequate audio system component grounding can all contribute to the reception of RFI and EMI. A properly grounded antenna body and radio chassis, as well as a shielded antenna coaxial cable with clean and tight connections will each help reduce the potential for reception of RFI and EMI.

REMOTE SWITCHES

Fig.13 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.

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. For complete circuit diagrams, refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.

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. For complete circuit diagrams, refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.