Part 2 of 5
AUDIO SYSTEMThere are radio systems available that communicate on the PCI bus. They use the bus for three reasons. First is to communicate trouble codes to the body control module, second is to control the remote radio switches located on the back of the steering wheel, and third is for use with the driver memory selection system. The radio stores two sets of station presets and can be recalled by pressing the optional memory select button (located on the drivers door). The midline will have 6 speakers and a 120 watt external amplifier. The Infinity I will have 7 speakers and a 240 watt external amplifier or with a in dash 4-disk CD Player. The Infinity II will have 9 speakers and a 360 watt external amplifier with indash 4-disk CD Player. Depending on the manufacturer, some systems have a Front/Rear channel system and others have a Left/Right channel system.
When troubleshooting output shorts or "output" error messages, the following applies:
On radios with out 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. The output DTC could refer to a front or rear output or a left or right output. The reason for the difference is the pairing of the output sections of the radio. Some are paired left and right, others are paired front and rear.
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.
These radios can be controlled via remote radio switches (optional). These switches are located on the back side of the steering wheel. They control volume, preset bank selection, seek and scan functions.
These functions are inputs to the body controller and can be read with the DRBIII(R) under "body" systems, sensor displays. The switches are a multiplexed signal to the BCM. The remote radio control circuit is a five volt line that is pulled to ground through different value resistors built into the switches. This causes a voltage drop to be seen by the body controller and it sends a specific message to the radio on the PCI bus line. The radio then responds to the message.
This circuit is fairly simple to troubleshoot. The circuit must be complete from the switches in the steering wheel to the BCM. The ground must be complete so that the switches can cause the voltage drop for the BCM to see. The circuit passes through the clockspring so continuity throught this device must be verified.
The new in-dash CD-changer is designed to fit into the existing cubby bin in the center stack. This new cartridge-less CD-changer is controlled by your radio, and allows you to individually load up to four discs at one time. However, due to its compact design, the CD-changer can only carry out one operation at a time. For example, you can not load a new disc while playing another at the same time. Each operation happens sequentially.
The radio unit installed with your system provides control over all features of the CD-changer with the exception of the CD load and eject functions, which are controlled by buttons located on the front of the CD-changer. The radio also supplies the power, ground, PCI Bus, left and right speaker output thru a single DIN cable. All features you would expect, such as Disc Up/Down, Track Up/Down, Random and Scan are controlled by the radio, which also displays all relevant CD-changer information on the radio display.
The CD-changer contains a Load/Eject button and an indicator light for each of the four disc positions. The individual light indicates whether a CD is currently loaded in that particular chamber of the CD-changer. Pressing the individual Load/Eject button for a particular chamber will eject a disc currently present in that chamber. If the chamber is currently empty, actuating the Load/Eject button will position that chamber to receive and load a new disc in that chamber.
BODY CONTROL MODULE
The Body Control Module (BCM) supplies vehicle occupants with visual and audible information and controls various vehicle functions. To provide and receive information, the module is interfaced to the vehicle's serial bus communications network (the Programmable Communication Interface or PCI bus). This network consists of the Powertrain Control Module (PCM), the Memory Heat Seat/mirror Module (MHSMM), Sentry Key Immobilizer Module (SKIM), the Transmission Control Module (TCM), the Electro/mechanical Instrument Cluster (MIC), the optional Overhead Travel Information System (OTIS), Occupant Restraint Control (ORC) module, optional Antilock Brakes (ABS), the radio remote CD-player, optional left and right airbag control modules, and the optional Automatic Temperature Control (ATC) display head. The (BCM) is operational when battery power is supplied to the module, ignition switch power is needed for ignition switched functions.
The body control module provides the following features:
Automatic headlamp and fog lamp
A/C switch status/evaporator temperature status
BCM diagnostic support
Central lock and unlock (VTSS only)
Climate Control (Automatic and Manual) system support
Door ajar switch status
Door Lock Inhibit (key in ignition or headlamps/park lamps ON)
Electronic Odometer Support
Fog Lamp Control
Headlamp multiplexing control
Headlamp, Park & tail lamps with battery save feature
Headlamp Time Delay
Illuminated Entry with "fade to OFF"
Interior lighting with battery save feature
Mechanical Instrument Cluster (fuel level, dim data, odometer & warning chime) support
Memory system (LHS and 300M)
Overhead travel information system
Power door lock multiplexing control
Rear Window Defogger Control
Remote Keyless Entry with Panic Mode
Remote power deck lid release
Remote radio control
Rolling door lock control (customer programmable)
Sentry key immobilizer
Speed proportional steering
Vehicle Theft Security System
Wiper Control (speed sensitive with return to park)
The BCM receives information over the PCI Bus from the PCM in order to support certain features.
The required information is as follows:
- Engine RPM
- Engine Temperature
- Injector on Time and Distance Pulses
- Vehicle Speed
- Charging System Failure, Engine Temperature Limp-In, VTSS Arming Status
- Engine Model
- "Check Engine" lamp status
The BCM provides the PCM with information on the A/C switch status and the VTSS status.
The LH has several customer programmable features which can be disabled or enabled by the customer.
CHIME SYSTEM
The chime system is comprised of an audible chime located internal to the BCM; and is dependent on various inputs to the BCM to operate. These inputs include key-in ignition switch, exterior lamps, seat belt switch, and requests from the MIC to chime when some indicators are turned ON.
DOOR AJAR SYSTEM
The door ajar state is used as an input for various control modules on the vehicle. The DRBIII(R) will display the state of the door ajar switches in Inputs/ Outputs. It's important to note, that when a door is closed, the switch state on the DRBIII(R) will show OPEN, and when the door is open, the switch state will show CLOSED. During diagnosis, if a door is closed and the DRBIII(R) displays the switch state as CLOSED, it indicates a shorted door ajar circuit. If the door is open and the DRBIII(R) displays the switch state as OPEN, it indicates an open door ajar circuit.
CLIMATE CONTROL SYSTEMS
Automatic Temperature Control (ATC)
The body control module (BCM) provides automatic temperature control support both through PCI bus communications and through processing inputs to determine control for actuators and the blower motor. The BCM interfaces with the ATC control head over the PCI bus. Information on button activation, blower setting, and temperature setting are supplied to the BCM. In turn, the BCM supplies the ATC control head with mode information and indication lamp status. The BCM controls blower motor speed by providing a varying duty cycle of a fixed frequency output (pulse width modulation). There are 14 distinct blower speeds, plus a blower OFF signal. The body control module also controls the HVAC mode, temperature (blend air), and recirculation doors. This system is either fully automatic or fully manual control (no semiautomatic functions); however, the temperature blend door control is always automatically controlled based on sensor reading and comfort setting. The in-car sensor and the aspirator motor are now housed in the ATC control head.
Manual Temperature Control
The body control module interfaces with the a/c- heater control head via hardwired circuits. Information for the temperature setting is supplied to the body control module via a potentiometer. The rear defogger switch, A/C switch and the mode setting is supplied via a resistive multiplexed circuit. The system ON/OFF status is supplied by a dedicated circuit. The BCM drives the A/C and rear defogger indicator lamps via hardwire to the A/C heater control head.
HVAC BLEND, MODE, And Recirculation Door Operation
The trouble codes that indicate a stall failure or a feedback signal failure work together to show what is wrong with the HVAC system. The stall trouble codes mean that the body control module cannot force an actuator to the end of the HVAC unit door. Internal problems in the body control module will set other short-related codes. Having only stall trouble codes indicates that there is a problem with an open or short circuit in the wiring, a bad actuator, a bad HVAC unit door or connecting linkage. It is important that the operation of the HVAC door be checked if an actuator is removed. This can be checked by rotating each unit door shaft to confirm that the door will stop at both ends of travel. The actuator itself has no stops. It must have the HVAC unit door to stop travel to pass a stall test.
A feedback signal failure can occur on the blend or mode door. The body control module monitors the feedback signal to check the position of the actuator. The body control module not only checks the level of the signal but also how much the voltage changes.
A feedback failure can occur if there is a short or open circuit in the wiring, a bad actuator, a bad body control module, a bad HVAC unit door or connecting linkage. The easiest way to diagnose this is to use the DRB to actuate the blend or mode door. Note that the feedback voltage of the actuator should smoothly change as the actuator is moved. A sudden change in the feedback voltage to a 5.0-volt or a 0.0-volt level indicates the actuator is bad. A fixed feedback voltage that is less than 5.0 volts or greater than 0.0 volts without a stall failure, or a short failure indicates that the actuator, the HVAC unit door, or a connecting mechanical linkage is jammed thereby preventing movement. A feedback signal voltage that stays on 5.0 volts or 0.0 volts indicates a wiring or body control module problem. The feedback voltage should always be less than 5.0 volts and greater than 0.0 volts.
The feedback trouble code can also occur from lack of actuator travel. This can be checked by confirming that the feedback signal smoothly changes when the actuator is moved with the DRB. If the signal is OK, the door travel is not correct. The actuator must be removed and the HVAC unit door mechanically checked for proper operation. Typical problems that prevent door movement include screws dropped in the HVAC unit or warped doors. Replace any part that is found defective.
Rear Window Defogger
When the BCM receives a rear defogger request from the climate control head (either ATC or manual) the BCM will activate the rear window defogger relay for 15 minutes. If the BCM receives another rear defogger request while the relay is still activated, the relay will be de-activated. If the relay is allowed to time out (full 15 minutes), further requests during the same ignition ON period will cause the BCM to activate the relay for 7.5 minutes
EXTERIOR LIGHTING SYSTEM
Exterior Lighting Battery Saver
The BCM monitors the status of and controls the park lamp, head lamp and fog lamp relay's. If any exterior lamps are left ON after the ignition is turned OFF, the BCM will turn them OFF after 10 minutes.
Headlamp Delay
The headlamp time delay operates when the ignition switch is turned OFF while the headlamps are still ON, and the headlamps are then turned OFF within 45 seconds after the ignition is OFF. This will provide a 90-second time delay before turning OFF the headlamps.
Headlamp Switch
The headlight switch on LH vehicles use a multiplexed (MUX) circuit to the BCM. The BCM will then control the park lamp, head lamp and fog lamp relay's based on this input.
Fog Lamp Control
The body control module controls the operation of the fog lamp relay which controls the fog lamps. The fog lamps can only be ON if the park or low beam headlamps are ON. If the high beams are turned ON, the fog lamps will automatically be turned OFF.
Auto Headlamps
The headlamps and park/tail lamps will be activated by the BCM when the headlamp switch is in the auto mode. To activate the auto headlamps the BCM requires that: (1) the headlamp switch is in the 'A' position, (2) the engine is running, and (3) the light level sensed through the sun load sensor falls below the calibrated level.