2002 LAND ROVER DISCOVERY fuse box

BODY CONTROL UNIT
86-3-18 DESCRIPTION AND OPERATION
Self levelling suspension and ABS
The BCU communicates with the SLABS ECU for several functions:
lAn output is provided from the SLABS ECU to the BCU to provide the logic conditions for issuing the SLS audible
warning.
lThe BCU receives an input from the SLABS ECU relating to the raise/ lower command from the remote handset.

+ REAR SUSPENSION, DESCRIPTION AND OPERATION, Description - SLS.
Hill descent control
The BCU provides an output signal to the SLABS ECU for automatic transmission in neutral for HDC control. The
BCU checks the status of the ignition and 'gearbox state' inputs and provides a 'Neutral selected' output. If the ignition
is on and 'gearbox state' is Neutral, the 'Neutral selected' output is on, otherwise 'Neutral selected' is off.

+ BRAKES, DESCRIPTION AND OPERATION, Description.
Heated screens
The Heated Front Screen (HFS) is fitted for some market destinations and is operated from a non-latching switch
located on the instrument pack cowl. The BCU will only allow the heated front screen to operate when the engine is
running and controls the time-out period for switching the circuit off.
The heated front screen operation can also be controlled from the Automatic Temperature Control (ATC) ECU on
vehicles fitted with air conditioning.
The heated rear window will only function when the engine is running, and is operated by a non-latching switch on the
instrument pack cowl. The heated rear window can also be operated by the ATC ECU on vehicles fitted with air
conditioning.
Interior courtesy lamps
The BCU controls the operation of the interior courtesy lamps. The courtesy lamps are situated in the front, mid and
rear areas of the headlining.
Fuel flap actuator
The BCU provides an earth path to the fuel flap release solenoid to allow the fuel filler flap to be opened. This is only
allowed if the alarm system is not set and all other conditions have been satisfied. The fuel flap release switch is
located in the fascia switch pack and it receives a voltage supply from the passenger compartment fuse box.
Audible warnings
The BCU can request the instrument pack to generate an audible warning in response to conditions it has detected
and which need to be drawn to the driver's attention. One of six different audible warnings can be requested by the
BCU.
Sound request number Sound functions Priority (1 = lowest, 6 = highest)
0Off 1
1 Seat belt warning 6
2 Key-in warning 3
3 SLABS/ HDC warning 4
4 Transfer box in neutral warning 5
5 Lights on warning 2

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-21
Passive coil
The passive coil is located around the ignition key barrel. When the BCU detects that the ignition key has been turned
to the crank position, the vehicle's immobilisation system is activated and a signal is sent to the passive coil at a
frequency of 125 kHz. The magnetic field generated in the coil is induced in the remote transmitter to trigger a re-
mobilisation signal.
BBUS/ alarm sounder/ vehicle horn
The BBUS is an audible warning device which operates under the control of the BCU if the anti-theft system is
activated or the vehicle battery is disconnected. The unit contains its own internal battery power source which is
charged via a feed from the passenger compartment fuse box. The BBUS will not sound if the battery is disconnected
while the security system has not been set.
Some markets utilise an alarm sounder which operates independently or in conjunction with the vehicle horn if the
anti-theft system is triggered.
Security system status LED
The LED flashes when the anti-theft system has been set. There are four different flash rates dependent on mode of
operation or other system information.
Central door locking
The doors can be locked by the following methods:
lPressing the lock button on the remote transmitter.
lLocking the vehicle from the driver's door with the key.
lPressing the lower half of the central door lock switch.
lPushing the sill button down (will only lock that particular door).
lBy driving over 7 km/h (4 mph) – ( if the speed related locking function has been enabled).
The BCU will prevent locking if the logical conditions for locking are not satisfied. Conditions which will prevent door
locking include:
lDriver's door open.
lIgnition switch on.
lInertia switch tripped.
lVehicle is already superlocked.
A mislock may occur if the logical conditions are not met.
The doors can be unlocked by the following methods:
lPressing the unlock button on the remote transmitter
lUnlocking the vehicle from the driver's door with the key.
lPressing the upper half of the central door locking switch (not operational if the vehicle is superlocked).
lPulling the interior door handles (not operational if the vehicle is superlocked).
lInertia switch being triggered while the ignition is on and the security system is de-activated.
The BCU supplies information via the serial data bus to the IDM to energise the coil of the relays for each of the door
lock actuators.
The BCU normally checks the following inputs to determine lock/ unlock requirements:
lUnlock request.
lLock request.
lSuperlock request.
lSingle point entry request.
lLock passenger and rear doors request.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-23
The BCU checks the status of the following inputs to determine when to provide the rear window enable and sunroof
enable output signals:
lIgnition state.
lDriver's door open.
lPassenger 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:
lA stall condition exists (window has reached bottom of travel).
lWindow switch is repressed in either direction for more than 0.4
± 0.2 second.
lThe BCU has operated the motor for a period greater than 10
± 0.2 seconds.
A timeout function is included which allows the windows and sunroofs to be operated for a period of 44
± 1 seconds
after the ignition key has been removed from the ignition switch. The timeout function will be cancelled if the BCU
detects the following conditions:
lThe driver's door has been closed after the ignition has been switched off.
lAny door open after the ignition is switched off.
The preconditions are programmed into the BCU dependent on market specification.
The BCU does not directly control rear window operation, but it can request the IDM to remove the power feed to the
rear windows. The IDM enables power supply to be provided to the rear lift relay in the passenger fuse box. When the
relay coil is energised the relay contacts close and power is applied to the rear window motor. If the window lift
isolation switch located in the centre console is latched out, the earth path from the LH and RH rear door window
switches is broken and operation of the rear window motors through the use of the rear window switches is prevented.
Rear window operation using the console switches is not affected by the isolation switch.
In the event of a communications link failure occurring while rear window enable is on, the relay remains on until the
ignition switch is turned to the off position.

BODY CONTROL UNIT
86-3-24 DESCRIPTION AND OPERATION
Heated screens
The heated screen time-outs and logical operations are controlled by the BCU.
Heated front screen
The BCU provides an output to the heated front screen relay and a 'heated front screen active signal' for the heated
front screen warning lamp. The BCU uses the status of the following inputs to determine the appropriate logical
operations for this feature:
lIgnition state.
lEngine running (link from instrument pack).
lHeated front screen selected (non-latched button pressed).
If the ignition switch is not in position II, or the engine running signal is OFF, the heated front screen will not be active.
The heated front screen operation period and voltage supply is controlled by the BCU. The BCU receives a voltage
supply feed from the engine compartment fuse box and an ignition switched supply through a fuse in the passenger
compartment fuse box. When the heated front screen switch is operated, it completes a path to earth, signalling a
request for heated screen operation to the BCU. The BCU then supplies a feed to the heated front screen switch to
light the switch indicator, and earths the supply from the coil of the heated screen relay to turn the heated front screen
on. The BCU maintains a supply for a predetermined time (5 minutes), then opens the earth path after the time out
period to turn the heated screen off. During the timeout period, if the heated front screen switch is pressed a second
time, the circuit is also interrupted to turn off the supply to the heated front screen.
On vehicles fitted with air conditioning, the heated front screen is also operated by the ATC ECU when DEF (defrost)
is selected. In this case the ATC ECU provides the trigger signal to the BCU to turn the heated front screen circuit on
or, if it is already on, to re-start the time out period.

+ AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.
In the event of a communications link failure occurring while the heated front screen relay is on, the relay and lamp
will remain on until the ignition switch is turned off or the time-out period elapses or the heated front screen switch is
pressed.
Heated rear window
The heated rear window will only function when the engine is running, and is operated by a non-latching switch on the
instrument pack cowl.
The BCU provides a 'heated rear window enable output' and a 'heated rear window active warning lamp signal' based
on the logic status of the following inputs:
lIgnition state.
lEngine running (link from instrument pack).
lHeated rear window selected (non-latched button pressed).
If the ignition switch is not in position II, or the engine running signal is OFF, the heated rear window will not be active.
The heated rear window operation period and voltage supply is controlled by the BCU. The BCU receives a voltage
supply feed from the engine compartment fuse box and an ignition switched supply through a fuse in the passenger
compartment fuse box. When the heated rear window switch is operated, it completes a path to earth, signalling a
request for heated rear window operation to the BCU. The BCU then supplies a feed to the heated rear window switch
to light the switch indicator, and earths the supply from the coil of the heated rear window relay via the IDM to turn the
heated rear window elements on. The BCU maintains a supply for a predetermined time (15 minutes), then opens the
earth path after the time-out period to turn the heated rear window operation off. If the heated rear window switch is
pressed a second time, the circuit is also interrupted to turn off the supply to the heated front screen.
On vehicles fitted with air conditioning, the heated rear window is also operated by the ATC ECU when DEF (defrost)
is selected. In this case the ATC ECU provides the trigger signal to the BCU to turn the heated rear window circuit on
or, if it is already on, to re-start the time out period.

+ AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.
In the event of a communications link failure occurring while the heated rear window enable is on, the relay and lamp
will be de-activated.

BODY CONTROL UNIT
86-3-26 DESCRIPTION AND OPERATION
If the ignition switch is in the off or crank position, the rear wipers are not active and the rear wiper enable output is
switched off.
In the event of a communications link failure occurring while the rear intermittent wipe programme is in operation, the
rear wiper enable output is switched off.
Reverse gear wipe
The BCU changes the operation of the rear wiper when the front wiper is active and reverse gear is selected. The rear
wiper operation rate used when the preconditions have been satisfied depend on the prevailing front wiper operating
mode and the position of the rear wiper switch. If the rear wiper is on or the front wiper is operating at an intermittent
rate when reverse gear is selected, the BCU will operate the rear wiper continuously for 4 seconds via the IDM. After
the initial period, the rear wiper will operate at the same rate as the front wiper.
The BCU checks for the following inputs to determine when to provide the rear wiper enable signal if the vehicle is in
reverse gear:
lIgnition state.
lRear wiper switch.
lFront intermittent wiper rate.
lReverse gear selected.
lFront intermittent wiper switch.
lFront wiper switch state.
lFront wash/ wipe in progress flag.
In the event of a communications link failure occurring while the reversing wipe is in operation, the rear wiper enable
output is switched off.
Headlamp wash
The headlamp wash will only operate when the headlamps are on, and then only every third time the front windscreen
wash button is pressed. When the BCU operates the headlamp washers, it activates the washer pump relay for a
period of 500 ms. The BCU supplies an earth path for the coil of the power wash relay located in the engine
compartment fuse box when the washer function is selected.
The BCU checks for the following inputs to determine when to provide power to the headlamp power wash relay:
lIgnition state.
lFront washer pump switch.
lDipped beam.
lMain beam state.
If the ignition switch is in the off position, the headlamp power wash relay is also held off. if the ignition state is crank,
the headlamp power wash relay is switched off and the headlamp power wash counter is reset to 0.
In the event of a communications link failure occurring while the headlamp power wash relay in on , the relay remains
on until the 500 ms timer has completed, then the relay is switched off.
Electric seats
The BCU can be programmed to operate the electric seats according to one of three options:
lOption 1 – no electric seats.
lOption 2 – normal.
lOption 3 – operates with ignition only.
To determine when to provide an output to the passenger and drivers seat enable relay, the BCU checks the condition
of the following inputs:
lIgnition state.
lTransit mode.
lDriver's door open.

BODY CONTROL UNIT
86-3-30 DESCRIPTION AND OPERATION
Fog lamps
The BCU operates the rear fog lamps and the front fog lamps (where fitted) via the IDM. The BCU front fog lamp
operation can be programmed to operate under one of three set conditions. The BCU will ensure the logical conditions
are satisfied for the lamps to operate under the set conditions.
Front fog lamps
Front fog lamp operation is monitored by the BCU, which allows only the front fog lamps to operate when the side
lamps or headlamps are on. When the side lamps, headlamps or ignition switch is turned off, the BCU also switches
off the fog lamps. When the side or headlamps are switched on again, the front fog lamps will remain off unless the
front fog lamp switch is pressed to resume operation. If the rear fog guard lamps are selected on, switching off the
front fog lamps will also switch off the rear fog guard lamps.
When the fog lamp switch is operated, an earth path is completed and the BCU allows the fog lights to be switched
on providing the logical preconditions have been satisfied. The BCU then supplies a voltage supply to the fog lamp
relay, to illuminate the fog lamps.
The front fog lamps option can be programmed in one of three states dependent on market/ customer requirements,
these are:
lOption 1– not fitted.
lOption 2 – main beam no effect.
lOption 3 – off with main beam.
The BCU checks the status of the following inputs to determine the logic action for providing an output to the front fog
lamp relay:
lIgnition state.
lMain beam state.
lSide lamps.
lDipped beam.
lFront fogs selected (press button, not latched).
If the ignition state is crank the state of the front fog relay is memorised and the relay is switched off. Pressing the
front fog switch during cranking will not be recognised. When the ignition state returns to Ignition after cranking, the
memorised front fog relay state is restored. If the ignition is turned off, the front fog relay is turned off.
For option 3 configuration, if the main beam is turned on the state of the front fog relay is memorised and the relay is
switched off. Pressing the front fog switch while main beam is on will not be recognised. When the Main beam state
returns to OFF, the memorised front fog relay state is restored.
In the event of a communications link failure while the front fog relay is on, the front fog relay will be switched off.
Rear fog lamps
The rear fog lamps operation is monitored by the BCU, which only allows the rear fog lamps to operate when the side
lamps or the headlamps are on. When the side lamps, headlamps or ignition is switched off, the rear fog lamps are
also switched off. When the side lamps or headlamps are switched on again, the rear fog lamps will not switch on
again unless reselected by operating the rear fog lamps switch. If front fog lamps are fitted, the rear fog lamps will be
switched off if the front fog lamps are switched off.
A supply voltage to the rear fog lamps relay is provided from a fuse in the passenger compartment fuse box, then
through two electronic switches in the IDM. With the lighting switch in the side lamp or headlamp position, an earth
path from the coil of the rear fog lamps relay completes the circuit through the two switches in the IDM to switch the
rear fog lamps on when the BCU receives a request signal from the rear fog lamps switch to turn the circuit on.

ALARM SYSTEM AND HORN
DESCRIPTION AND OPERATION 86-4-5
Description
General
The anti-theft system deters the theft of the vehicle with both active and passive systems. The active systems monitor
the vehicle perimeter and, in some markets the vehicle interior, for intrusion. If the system detects intrusion, an alarm
sounds. The passive systems include a vehicle immobiliser as well as protection against intrusion through super
locking the doors. The vehicle is immobilised whenever the ignition key is removed from the ignition switch. Super
locking prevents the interior door handles from opening the doors. In addition, there are many features and functions
that enhance system operation.
It is possible to perform the various functions associated with the anti-theft system remotely. To accomplish this, the
handset generates a radio frequency when the lock button or unlock button is depressed. This signal is transmitted
to the Body Control Unit (BCU) via a receiver located in front of rear sunroof beneath the headlining. Precise alignment
of the handset to the receiver is not necessary. The approximate operating range between the handset and the
receiver is 10 metres (33 feet).
It is important to understand the configuration of the system on each particular vehicle. There are many
different combinations of features with dedicated operating modes. System configuration for each vehicle
can be determined using TestBook.
The anti-theft system is controlled centrally by the BCU, which is located below and behind the passenger glovebox.
A serial communication link communicates between the Intelligent Driver Module (IDM) located within the fusebox,
the BCU and the LED located in the instrument panel.
The state of the alarm is stored in the BCU. If the battery is disconnected while the alarm is armed, the alarm will be
triggered when the battery is reconnected.
NOTE: Disconnecting the battery while the alarm is armed triggers the alarm. Always disarm the alarm system before
disconnecting the battery.
The BCU also receives inputs from the following components:
lIgnition key in sensor.
lIgnition switch.
lFuel cut off switch.
lFuel flap release switch.
The BCU also interacts with the following components:
lStarter relay.
lVehicle horns.
lDirection indicators.
lFuel flap release actuator.
lCourtesy lamps.

ALARM SYSTEM AND HORN
86-4-8 DESCRIPTION AND OPERATION
Door lock actuators
The door lock actuators are D type latches. The door locks allow the vehicle to be locked/unlocked and super locked
to prevent access to the vehicle via the interior door handles.
Input/Output
The driver's door lock actuator has a dedicated 12 volts power supply from the passenger compartment fuse box to
energise the locking action of the door lock actuator. The passenger and rear door lock actuators share a 12 volts
power supply from the passenger compartment fuse box to energise the locking action of the door lock actuator.
To perform the super locking action all the door lock actuators receive a 12 volts power supply from the passenger
compartment fuse box.
To perform the unlocking action for all the doors, a 12 volts power supply from the passenger compartment fuse box
is supplied to the door lock actuators.