Element 2WD L4-2.4L (2003)
Body Control Systems: Description and Operation
System Descriptions
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 system DTCs, Mode 2 for input lines)
The system controls the function of these circuits:
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Entry light control (ignition key light and ceiling light)
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Wiper/washer (intermittent wipe and park functions)
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Interlock system
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Power Door Lock
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Gauge assembly, (temperature gauge, and indicators)
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HVAC (Compressor and fan control)
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Key-in reminder
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Lights-on reminder
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Seat belt reminder
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).
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The digital signals are sent from the transmitting unit to the receiving unit as serial data signals.
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The transmitted signal is converted to a switch signal at the receiving unit, and it operates the related component or performs a function
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There are exclusive communication lines between the ECM/PCM, the gauge assembly, and the under-dash fuse/relay box.
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 functioning (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, a door is unlocked), the related control unit in the sleep mode immediately wakes up and
begins to function.
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When the ignition switch is turned OFF, and the driver's or front passenger's door is opened, then closed, there is about a 40 second delay before
the control unit goes 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 draw is reduced from 200 mA to less than 35 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
ignores the signal from the malfunctioning control unit and allows the system to operate normally.
