Honda 2004 Odyssey Service Manual page 1922

System Descriptions
The multiplex control system has four internal
functions:
• Multiplexing (send multiple signals over shared
wires)
• Wake up/sleep modes (runs at full power only on
demand to reduce battery draw)
• Fail-safe (fixes or ignores faulty signals)
• Self-diagnosis (Mode 1 for the system, Mode 2 for
input lines)
The system controls the function of the following
circuits
• Engine Oil Pressure Indicator
• Seat Belt Reminder
• Lights-on Reminder
• Key-in Reminder
• Key Light Timer
• Dash Lights Brightness Control
• Entry Light Control (EX and EXL models)
• Automatic Lights-off (EX and EXL models)
• Power Window (including key-off timer operation)
• Wiper/Washers (including speed sensitive
intermittent wiper)
• Keyless/Power Door Locks
• Interlock
• Factory Security Alarm System ('01-04 EX and '02-04
EXL models)
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.
• 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.
• The transmitted signal is converted to a switch signal
at the receiver unit, and it operates the related
component.
• There are exclusive communication lines between
each of the multiplex control units:
– Door Driver's (between the door and the driver's
multiplex control units) Wire color: BRN
– 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.
• 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.
• 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.
• When the ignition switch is turned OFF, and driver's
or front passenger's door is opened then closed,
there is about a 10 second delay before the control
units go from the wake-up mode to the sleep mode.
• If any door is open, the sleep mode will not function.
• If a key is in the ignition switch, the sleep mode will
not function.
• If one of the key cylinder switch inputs is shorted, the
sleep mode will not function.
Fail-safe
To prevent improper operation, the multiplex control
system has a fail-safe function. In the fail-safe mode,
the output signal is stopped 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
stops the output signal when there is any CPU
malfunction, and a software fail-safe function that
ignores the signal from the malfunctioning control unit
and allows part of the system with no defect to operate
normally.
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