Discovery II (LT) V8-4.6L (2003)
/v8-4.6l/Page-705002.png)
Battery supply to the IDM is provided through the inertia switch and a 10 A fuse in the engine compartment fuse box. If the inertia switch contacts are
closed battery voltage is available at the IDM; if the inertia switch contacts are open there is no battery supply to the IDM. The supply condition of the
IDM is signalled to the BCU via the serial bus. If the inertia switch is operated (contacts open) the change in state is detected by the BCU which
unlocks the doors if the ignition switch is in position II and the alarm is not set.
The BCU is earthed through a hard-wire connection.
Inputs and Outputs
The BCU and IDM process inputs and provide the necessary outputs for control and operation of the vehicle's 'body systems.
BCU inputs
The BCU processes signals received from the following components:
^
Door latch switches.
^
Driver's door key lock/unlock switches.
^
Bonnet activated security system.
^
Volumetric sensors.
^
Central Door Locking (CDL) switches.
^
Remote transmitter (via receiver unit).
^
Inertia fuel cut-off switch.
^
Ignition switch.
^
Fuel flap release switch.
The input voltages (Vin) for BCU digital signals are defined as follows:
^
Logic 1 when Vin > 6 V.
^
Logic 0 when Vin < 2 V.
BCU input voltages between 2 and 6 volts are indeterminate and cannot be guaranteed.
Analogue input voltages are measured as a ratio with respect to battery voltage.
BCU outputs
The BCU processes the input signals it receives and uses the information to determine the control outputs that need to be established for any given set
of conditions. The BCU provides controlled outputs for the following systems:
^
Interior courtesy lamps.
^
Fuel flap release actuator.
^
Anti-theft status LED.
^
Engine Control Module.
^
Door lock actuators.
^
Direction indicators and hazard warning lamps.
^
Headlamps.
^
Alarm sounder.
^
Vehicle horns.
^
Battery backed sounder.
^
Starter relay.
^
Passive re-mobilisation exciter coil.
Simultaneous switching of outputs in different units is limited by the bus transfer time, but the skew is no longer than 100 ms for either the BCU or the
IDM. When the processor is reset, all outputs are switched off until the inputs have been read for the first time to check current condition.
