RL V6-3474cc 3.5L (1998)
Information Bus: Reading and Clearing Diagnostic Trouble Codes
Description of On-Board Diagnostics
Multiplex Communication Functions
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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 (from the door to the driver's multiplex control units) Wire color: BRN/YEL
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Driver's Passenger's (from the driver's to the passenger's multiplex control units) Wire color: BRN/WHT
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Passenger's Driver's (from the passenger's to the driver's multiplex control units) Wire color: RED/YEL
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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 Functions
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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 done (for example, a door is unlocked), the related control unit in the sleep mode wakes up and begins to function at
once. 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, there is about a 30 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.
Fail-safe Functions
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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).
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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 ignores the signal from the malfunctioning control unit and allows the system to operate normally.
