Accord EX Coupe V6-3.0L (2001)
Information Bus: Description and Operation
System Description
The multiplex Control System has four internal functions:
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Multiplexing (send multiple signals over shared wires)
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Wake up/sleep (runs at full power only on demand to reduce battery draw)
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Fail-safe (fixes or ignores faulty signals)
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Self-diagnosis (Mode 1 for the system, Mode 2 for input lines)
The system controls the function of the following circuits
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Engine Oil Pressure Indicator
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Seat Belt Reminder
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Lights-on Reminder
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Key-in Reminder
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Key Light Timer
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Dash Lights Brightness Control
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Entry Light Control (EX, SE) (ignition key light and ceiling light)
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Automatic Lights-off (EX)
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Power Door Locks
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Power Window (including key-off timer operation)
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Wiper/Washer (including speed responsive intermittent wiper)
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Keyless Entry/Security Alarm (EX, SE)
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Interlock system.
How the Circuit Works
The conventional portion of the electrical system carries DC (or A/C) power through separate wires to each component. The multiplex portion of the
system, however, sends digital signals between control units through shared wires to reduce the number and weight of wire harnesses. The input signals
from each switch are converted to digital signals within the receiving multiplex control unit. The digital signals are sent from one multiplex control unit
to another as serial data over dedicated communication lines. When the appropriate control unit receives the digital signal, it converts it back to a switch
signal and operates the related components.
Multiplex Communication
To reduce the number of wire harnesses, digital signals are sent via shared multiplex communication lines rather than sending normal electrical signals
through individual wires.
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The input signals from each switch are converted to digital signals at the central processing unit (CPU). The digital signals are sent from the
transmitter unit to the receiver unit as serial signals.
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The transmitted signal is converted to a switch signal at the receiver unit, and it operates the related component.
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There are exclusive communication lines between each of the multiplex control units:
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Door <-> Driver's (between the door and the driver's multiplex control units) Wire color: BRN
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Driver's <-> Passenger's (between the driver's and the passenger's multiplex control units) Wire color: PNK
The control units always communicate via these lines when the system is operating, and they stop communicating when the system is OFF.
Wake-up and Sleep
The multiplex control system has "wake-up" and "sleep" functions to decrease parasitic draw on the battery when the ignition switch is OFF.
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In the sleep mode, the multiplex control unit stops the functions (communication and CPU control) when it is not necessary for the system to
operate.
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As soon as any operation is requested (for example, door is unlocked), the related control unit in the sleep mode immediately wakes up and begins
to function. This control unit also sends a wake-up signal to the other control units via the communication lines.
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When the ignition switch is turned OFF, and driver's or front passenger's door opened, there is about a 10 seconds delay before the control units
go from the wake-up mode to the sleep mode.
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If any door is open, the sleep mode will not function.
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If a key is in the ignition switch, the sleep mode will not function.
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When in sleep mode, the current draw is reduced from 70 - 80 mA to less than 10 mA.
Fail-safe
To prevent improper operation, the multiplex control system has a fail-safe function. In the fail-safe mode, the output signal is fixed when any part of the
system malfunctions (for example, a faulty control unit or communication line).
Each control unit has a hardware fail-safe function that fixes the output signal when there is any CPU malfunction, and a software fail-safe function that