Discovery II
BODY CONTROL UNIT
86-3-22 DESCRIPTION AND OPERATION
Electric windows and sunroof
Three modes of operation are available:
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Driver cancel – the front windows, rear windows and sunroof will be disabled 44 seconds after the driver's door
is opened.
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All cancel – The front windows, rear windows and sunroof will be disabled 44 seconds after any door is opened.
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No cancel – the front windows, rear windows and sunroof will be disabled when the ignition is turned off.
The BCU will allow window and sunroof operation when the ignition key is in position II. The BCU provides a voltage
to the window control switches. When the switches are pressed, they provide a path to earth to complete the circuit
and initiate window operation. Window and sunroof operation is suspended when the ignition switch is in the crank
position.
For front window operation, the BCU checks the status of the following inputs:
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Ignition state.
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Driver's door open.
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Passenger or rear door open.
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Front right window down.
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Front right window up.
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Front left window down.
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Front left window up.
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Right window stall detect.
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Left window stall detect.
The front window motors are directly connected to the BCU by two wires. Each wire can be used as a feed or return,
dependent on the required direction for motor operation (open or close). The BCU provides the following outputs:
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Right window up.
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Right window down.
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Left window up.
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Left window down.
The electric front windows are enabled when the ignition switch is in position II and is disabled if the ignition switch is
moved to the crank position.
The BCU checks the status of the following inputs to determine when to provide the rear window enable and sunroof
enable output signals:
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Ignition state.
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Driver's door open.
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Passenger or rear door open.
The rear window enable and sunroof enable lines are on when the ignition switch is in position II, and are switched
off if the ignition switch is moved to the crank position.
The BCU monitors the circuit current draw when the windows are operating to detect the occurrence of a stall
condition. If the BCU determines that the window has stalled, it will cut the power supply to stop the operation of the
window motor. The BCU only starts to check for a stall condition after the window has been operating for 500 ms. This
delay period enables the initial current surge to pass and eliminates false detections of window stall. A stall condition
is activated when a nominal current value is exceeded for a period greater than 300 ms.
If the BCU detects that it has been operating the same window motor in one direction for more than 10
±
0.2 seconds,
without the BCU detecting a stall condition or the control switch being released, it will automatically stop operation of
the window motor (timed out). Window operation can resume when the window switch is released and pressed again.
If the window was operating in one touch mode, the window operation will resume on the next press of the window
switch.
One touch mode automatically lowers the window to its fully open position, without the need for the window switch to
be kept pressed for the duration of the window travel. One touch mode is initialised if the window switch is pressed
for a period of less than 0.4
±
0.2 second. One touch mode continues to lower the window until the BCU detects:
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A stall condition exists (window has reached bottom of travel).
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Window switch is repressed in either direction for more than 0.4
±
0.2 second.
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The BCU has operated the motor for a period greater than 10
±
0.2 seconds.
