1999 LAND ROVER DISCOVERY lock

BODY CONTROL UNIT
86-3-20 DESCRIPTION AND OPERATION
In some markets, when the alarm is triggered the BCU also activates the direction indicators, in phase with the audible
warning, to provide an optical warning of a theft attempt. The activation period of the optical alarm is 25 to 30 seconds.
The duty cycle of the optical warning is 50:50 ± 10%.
The alarm system relies upon the vehicle battery for power. However, the BCU remembers the status of the security
system if it loses battery supply. If the security system was in a set condition when battery supply was lost the BCU
will trigger the alarm and initiate a visual warning by flashing the hazard lamps when the battery voltage is restored.
On vehicles with a BBUS fitted, the BBUS will sound if the battery is disconnected while the alarm system is set.
Door switches
The BCU uses the door latch switches to indicate if a door is open or closed. The BCU provides power to all door latch
switches; the switches are in the 'normally open' condition when the doors are shut. When a door is opened, the door
switch contacts are closed and the circuit is earthed, signalling a change in state to the BCU. All doors except the
driver's doors are connected in parallel, so the BCU will recognise a passenger door has been opened but will not be
able to distinguish which one. The driver's door has a dedicated signal line which enables the BCU to detect if the
driver's door has been opened or closed.
Door lock actuators
The CDL system has the facility to enable superlocking. All door lock actuators are controlled by the BCU via the IDM.
The driver's door is controlled separately from all other doors, enabling functions like single point entry and key
access.
Driver's door key lock and unlock switches
The BCU uses the driver's door key lock and unlock switches to activate and deactivate the security system. The
driver's door lock is also used for entering the EKA code.
Two separate switches are incorporated into the key lock assembly of the driver's door. The switches are normally
open and the BCU provides a separate power supply to each. The BCU is signalled when a circuit is earthed enabling
it to determine the direction in which the lock has been turned.
Bonnet switch
The bonnet switch is powered from the BCU and is used as a logical input for operation of the security system. The
switch is normally open with the bonnet closed, when the bonnet is opened the switch contacts close to complete a
circuit to earth and signal the change in state to the BCU.
Key-in sensor
When the ignition key is inserted into the lock barrel the key-in sensor contacts close and supply a signal to the BCU.
The BCU monitors the ignition switch for a change in state and triggers the alarm if it receives an ignition signal before
it receives an alarm disarm signal.
Another feed to the ignition switch is provided by the BCU to provide switch illumination.
A key-in warning can be enabled or disabled. When the key-in warning is enabled, an audible warning is generated
if the ignition key is in and the driver's door is opened.
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.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-21
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.
The following outputs are generated by the BCU dependent on the prevailing logic conditions and the input requests
the BCU has detected:
lUnlock all doors enable.
lLock passenger and rear doors enable.
lSuperlock all doors enable.
lLock driver's door enable.
All lock/ unlock pulses have a duration of 800 ms.
Input/Output logic for door lock/unlock
To determine if the vehicle speed is appropriate for enabling speed related locking, the BCU uses the vehicle speed
signal supplied over the serial data bus from the instrument pack.
Output/Request Superlock all
doors enableUnlock all doors
enableLock driver's
door enableLock passenger
and rear doors
enable
Unlock request 0 1 0 0
Lock request 0 0 1 1
Superlock request 1 0 1 1
Single point entry request 0 1 0 1
Lock passenger and rear doors request 0 0 0 1

BODY CONTROL UNIT
86-3-26 DESCRIPTION AND OPERATION
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.
The electrically controlled seats are operated when the ignition switch is in position I or II or for a predetermined period
when the driver's door is open. If the ignition state is in crank, the seat enable relay is off. If the ignition state is off and
the driver's door open input is off, the seat enable relay is off. If the ignition state is off and the driver's door open input
is on and transit mode is on, the seat enable relay output is off.
The power supply to each seat switch pack is powered from a power seat relay located on the underside of each seat
frame. The feed from the relay is protected by a fuse located in a satellite fuse block located adjacent to the power
seat relay. The fuse block also contains two additional fuses which are used to protect the feeds to the lumbar pump
and solenoid.
With the ignition switch in position I or II or the driver's door open, the BCU provides an earth path for the coils of the
LH and RH power seat relays, energising the relays and closing the contacts. If the driver's door input signal is on for
longer than 45 seconds with the ignition switched off, the seat enable relay is switched off.
Direction indicators and hazard warning lamps
The BCU supplies reference voltages for the LH and RH indicators. When the direction indicator switch is used to
select the LH or RH indicator position, an earth path is completed which signals the BCU that a request for direction
indicator operation has been made. The BCU then communicates this request to the IDM which supplies an earth
path for the coil of the relevant relay (LH or RH indicator relay). When the relay coil is energised, the relay contacts
close and a voltage supply is provided via a resistor to the relevant direction indicators. The IDM controls the timing
of the flash operations by continually removing and restoring the earth path to the direction indicator relay coil.
The BCU checks for the following inputs for performing the logic operations associated with the direction indicator
lamps:
lIgnition state.
lRH indicators selected.
lLH indicators selected.
lHazards selected.
lInertia switch hazard request.
lOne short indicator flash request (anti-theft system arming).
lTwo short indicator flash request (superlocking).
lOne long indicator flash request (anti-theft system disarming).
lAlarm flashing indicators (anti-theft alarm triggered).
The following outputs are provided by the BCU as a result of the inputs received and the logical operations performed:
lRH indicators enable.
lLH indicators enable.
lDirection indicator left message (link to IDM).
lDirection indicator right message (link to IDM).
Direction indicator lamp failure detection
The BCU uses the following logic inputs to determine if there is a direction indicator bulb failure or if the presence of
a trailer is detected. The BCU uses the information to decide which output to enable at any particular instance:
lRight direction indicators requested.
lLeft direction indicators requested.
lRH indicators current sense.
lLH indicators current sense.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-27
If a direction indicator bulb failure or a trailer presence is detected, the following outputs can be generated depending
on the BCU logic states:
lTrailer detected.
lBulb failure detected.
lDirection indicator short circuit.
lDirection indicator relay stuck.
The BCU can be configured whether or not to provide bulb failure warnings.
When the direction indicators are operating, instrument pack direction indicators flash in sequence with the exterior
direction indicators. If a failure of an indicator bulb occurs, the corresponding instrument pack indication lamp will flash
quickly to warn of the problem.
The IDM monitors the current drawn through the circuit to detect for the occurrence of a lamp failure. If an indicator
lamp fails, the IDM detects the drop in current drawn through the resistor and operates the indicator relay at a faster
speed. The fast flash is demonstrated on the instrument pack direction indicator warning lamps to bring attention to
the driver that a direction indicator bulb failure has occurred. The current sense for the related indicator lamps (RH or
LH) are checked when a direction indicator request has been made that lasts for at least 160 ms. The current level
sensed is relative to the number of working bulbs and determines the request generated by the BCU.
The output is signalled to the instrument pack using the serial communications link. If the hazard warning lamps are
operating, both sets of direction indicators are checked using the current sensing functions to check the number of
bulbs on each side of the vehicle.
If the BCU detects that a direction indicator request has not been made, but one or other of the current sense inputs
indicate that current is flowing, a 'Relay stuck' output is generated.
Hazard lamps
The BCU controls the operation of the hazard warning lamps via the IDM and dedicated relays. The hazard warning
lamps are activated under the following conditions:
lThe vehicle is locked and the security system is set (the hazard warning lamps flash three times if the
superlocking feature is used, once if not).
lThe vehicle is unlocked (the hazard warning lamps flash once for a duration of two seconds).
lThe anti-theft alarm system is triggered (the hazard warning lamps flash in phase with and for the duration of the
audible warning).
lThe hazard warning switch is pressed (the hazard warning lamps flash until the hazard warning switch is pressed
for a second time).
lThe inertia switch is triggered (the hazard warning lamps flash until the inertia switch has been reset).
The hazard warning lamp operation may differ dependent on market and customer configuration options.
The hazard warning lamps are operated from a latching pushbutton switch located on the fascia. When the switch is
pressed, both left and right indicator lamps in the instrument pack flash to show that the hazard warning lamps are
operating and all hazard warning lamps flash simultaneously. If a trailer is fitted, the ICM detects this and a trailer
symbol in the instrument pack also flashes to show correct operation of the trailer direction indicators and hazard
warning lamps.
The BCU supplies a reference voltage to the hazard warning switch. When the hazard warning switch is operated an
earth path is completed which signals the BCU that a request for hazard lamp operation has been made. The BCU
then sends a signal to the IDM via the serial data bus to communicate the request. The IDM supplies an earth path
for both direction indicator relay coils simultaneously so that the hazard warning lamps are turned on concurrently.
The IDM controls the timing of the flash operations by continually removing and restoring the earth path to both
direction indicator relay coils simultaneously.
Number of working bulbs Request generated
3 Trailer detected
2 None (bulbs okay)
1 Bulb failure detected
0 Direction indicator short circuit detected

BODY CONTROL UNIT
86-3-28 DESCRIPTION AND OPERATION
Courtesy headlamps
This feature activates the headlamps for 30 seconds when the lock button on the remote transmitter is held down for
longer than 1 second. The headlamps will extinguish if the BCU receives either a lock or an unlock signal from the
remote transmitter.
The BCU checks the status of the following inputs to determine the correct qualifying conditions for requesting
courtesy headlamps:
lIgnition state.
lRemote locking request.
lRemote unlocking request.
lLazy locking request.
If the ignition is off and a lazy locking request is received, the courtesy headlamps are switched on and an internal
timer is turned on in the BCU which operates for 30 seconds. If the 30 second timer expires or a request for remote
locking or remote unlocking is received, the courtesy headlamps will be turned off.
When main beam is selected, the IDM also provides a signal to the instrument pack to switch on the main beam
warning lamp. An additional signal 'main beam indicator disable' is used to prevent the daylight running lamps
illuminating the main beam indicator when the main beam is in the daylight running lamp state and the main beam
indicator disable signal is on.
Lights on alarm
The lights on alarm in the instrument pack operates when the driver's door is open and the side lamps or headlamps
are on. The system uses inputs from the driver's door switch and the lighting switch to determine the logical conditions
that need to occur for switching on the alarm. The BCU carries out the logic operation and communicates with the
instrument pack using the serial data bus; the instrument pack will be requested to sound the alarm if the logic inputs
indicate that the driver's door is open with the lights still on.
Supply voltage is provided through the lighting switch to the IDM which acts as the signal line to indicate that the lights
are on for the logic circuits in the IDM and BCU. When the driver's door is opened, a second feed is supplied to the
BCU through the driver's door switch to indicate the condition. In this logic condition (lights on and driver's door open)
the BCU signals the instrument pack to operate the audible warning. If the lights are switched off or the driver's door
is closed the logic condition will be changed and the audible warning will be switched off.
Daylight running lamps
The BCU operates the daylight running lamps (where fitted) via the IDM. The daylight running lamps option can be
programmed in one of three states dependent on market/ customer requirements, these are:
lOption 1– no daylight running lamps.
lOption 2 – on with main beam off.
lOption 3 – on with main and dipped beam off and gearbox not in Park.
The BCU will ensure the logical conditions are satisfied for the lamps to operate under the set conditions. The BCU
checks the status of the following inputs to determine the logic action for providing an output to the daylight running
lamp relay:
lMain beam state.
lEngine running (link from instrument pack).
lDipped beam.
lGearbox state.
A voltage supply is fed to the coil of the daylight running lamp relay and the IDM. When the preconditions are satisfied
for daylight running lamp operation, the BCU sends a signal for the IDM to complete the circuit to earth to switch on
the daylight running lamps. The logical inputs are checked to ensure that the engine is running before switching the
relay to turn on the daylight running lamps. The engine running signal has to be present for at least 2 seconds before
the daylight running lamp relay can be switched on.
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.

BODY CONTROL UNIT
86-3-30 DESCRIPTION AND OPERATION
Interior courtesy lamps
To determine when to provide an interior courtesy lamps enable output, the BCU checks the following input
conditions:
lIgnition state.
lTransit mode.
lDriver's door open.
lPassenger or rear door open.
The courtesy lamps operate at full brightness when they are first switched on. The BCU then gradually dims the lamps
(fade-out) before completely switching them off. Fade-out occurs over a period of two seconds following the logical
control signal to turn off the lights. When a door is opened, the BCU provides earth paths from the interior lamps, the
load space lamp and the ignition switch illumination. The following table lists the courtesy lamps operation and
duration for holding the lamps on that occurs after the BCU has detected a condition that signals the courtesy lamps
should be switched on:
Instrument pack
The BCU communicates with the instrument pack to provide a range of functions.
Odometer update
The BCU can be programmed for one of two options:
lOption 1 – no odometer error warning.
lOption 2 – odometer error warning.
In order to provide an LCD flash request to the instrument pack via the communications link, the following inputs are
checked:
lIgnition state.
lInstrument pack odometer value (via the communications link).
lBCU odometer value.
The function is only active when the ignition state is on. The maximum allowed value is 999,999 miles (1,608,999
km).If the instrument pack odometer value is greater than the maximum allowed value, the maximum value is
assumed. The BCU odometer value is stored in EEPROM. If 16 identical values of the instrument pack odometer
reading is received consecutively, the instrument pack odometer value is compared with the BCU odometer value. If
the consecutive readings from the instrument pack differ, the BCU odometer value is incremented accordingly. If the
BCU odometer value is less than the instrument pack odometer value by up to 10 km, the BCU odometer value is set
equal to the instrument pack odometer value.
If the odometer warning option is enabled, and the contents of the instrument pack odometer value buffer is identical
to, or greater than BCU odometer value ± 10 km, the BCU sends an LED flash request to the instrument pack.
In the event of a communications link failure, this function will be unable to operate.
Control signal Additional conditions Duration
Door open - 10 minutes
Unlock signal from remote transmitter All doors closed and ignition switch not in
position III1 minute
Unlock signal from the driver's door lock All doors closed and ignition switch not in
position III1 minute
Ignition switch turned from position II or III to
position 0All doors closed 1 minute
Door changed from open to closed All other doors closed and ignition switch not
in position III15 seconds
Ignition switch in position III - Timer cancelled
BCU receives a lock command - Timer cancelled
Vehicle has transit mode enabled - 15 seconds on all occasions

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-31
Gear position indicator illumination
On automatic gearbox models, two variations of illumination for the gear position indicators on the selector lever can
be programmed into the BCU. In option 1, illumination is provided when the ignition is on. In option 2, illumination is
enabled when the ignition is on and the side lamps are off.
Starter relay
The BCU checks the status of the following inputs and internal BCU conditions to determine whether or not to provide
an output to enable the starter relay:
lAutostart inhibit (vehicles with automatic gearbox only).
lSecurity start inhibit (immobilisation check).
lEngine running (link to instrument pack).
lEEPROM locked (internal check).
lIDM and BCU matched.
When the BCU receives a crank signal from the ignition switch, an earth path is completed to the starter relay coil,
provided that the security system has been de-activated. If the ECM has not received a valid unlock/ remobilise signal,
the starter relay will be disengaged and the engine stopped. The BCU also receives an engine running signal from
the instrument pack, so that if the ignition key is turned to the crank position while the engine is running, the starter
motor relay will not be engaged.
If the logic conditions are correct to allow starter operation, the completion of the earth path from the starter relay coil
to the BCU energises the coil and the relay contacts close to supply battery power to the starter motor.
When the ignition switch is released from the crank position, the power supply feed from the ignition switch to the
starter relay coil is interrupted and the relay contacts open to prevent further battery feed to the starter motor.
If a communications link failure is experienced, the BCU will be prevented from detecting the 'engine running'
condition and the BCU will default to assume that the engine is not running.
Cruise control
The Neutral/ Reverse/ Park/ Brake selected output is used by the cruise control system. The BCU checks for the
following inputs:
lIgnition on.
lGearbox state.
lBrake switch activated.
For vehicles with manual transmission, Neutral/ Reverse/ Park/ Brake selected output is on if the ignition is on and
brake switch activated is on. Otherwise, the Neutral/ Reverse/ Park/ Brake selected output is off.
For vehicles with automatic transmission, the Neutral/ Reverse/ Park/ Brake selected output is on if the ignition is on
and brake switch activated is on, or if the ignition is on and 'gearbox state' is in Neutral, Park or Reverse. Otherwise
Neutral/ Reverse/ Park/ Brake selected output is off.
Shift interlock (where fitted)
On automatic gearbox models, the BCU and IDM combine to operate a shift interlock solenoid, so that the gear
selector lever can only be moved when certain logical conditions have been satisfied. Operation of the interlock may
be affected, if the battery becomes discharged.

+ AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Description.
When the gear selector lever is in the Park position and the ignition is off, an interlock solenoid is de-energised, locking
the gear selector lever in the Park position.
The gear selector lever can only be moved from the Park position when the ignition is switched on and the brake pedal
is depressed. When these conditions are satisfied, the brake pedal switch signal is received by the BCU which then
signals the IDM to energise the interlock relay. When the interlock relay is energised, the interlock solenoid is
operated, unlocking the gear selector lever.
When the brake pedal is released, the feed to the BCU is removed and the shift interlock solenoid is de-energised.
The locking mechanism controlled by the solenoid will lock the gear selector lever once it is returned to the Park
position.

BODY CONTROL UNIT
86-3-32 DESCRIPTION AND OPERATION
The shift interlock option can be programmed in one of three states dependent on market/ customer requirements,
these are:
lOption 1– not fitted.
lOption 2 – normal operation.
lOption 3 – inhibit transfer box.
The BCU checks the status of the following inputs to determine the logic action for employing the shift interlock
solenoid:
lBrake switch activated.
lIgnition state.
lGearbox state.
In the event of a communications link failure, the shift interlock solenoid enable is switched on for 1 minute every time
the ignition is switched on and switched off when the ignition is turned off.
Ignition interlock (where fitted)
On automatic gearbox models, when the ignition key is inserted in the ignition switch, the ignition key-in switch
contacts close to supply a signal to the BCU to indicate the presence of the key in the switch and provide a supply
feed to the ignition interlock solenoid. If the gear selector lever is in a position other than Park, or the 'transfer box
neutral selected' is on, the BCU will supply an earth path to complete the ignition interlock circuit and cause the
interlock solenoid to be engaged. With the interlock solenoid engaged, removal of the ignition key is prevented. The
BCU will open the circuit, to allow removal of the ignition key, only when the gear selector lever is in the Park position
and the transfer box is in either high or low range.
The ignition key interlock option can be programmed in one of three states dependent on market/ customer
requirements, these are:
lOption 1– not fitted.
lOption 2 – normal operation.
lOption 3 – inhibit transfer box.
The BCU checks the status of the following inputs to determine the logic action for operating the ignition key interlock
solenoid:
lTransfer box neutral selected.
lGearbox state.
lTransit mode.
When the transit mode is on, the ignition key interlock solenoid is off.
Transfer box interlock (where fitted)
The transfer box interlock is controlled by the IDM to prevent transfer box shifter operation unless certain
preconditions have been satisfied.
The transfer box interlock prevents the transfer box being shifted from High or Low to neutral with the ignition key
removed from the ignition switch. When the BCU senses that the ignition key is removed from the ignition switch, it
signals the IDM via the serial data bus. The IDM then provides an earth path for the coil of the transfer box relay,
energising the relay coil and closing the relay contacts to provide a voltage supply to the transfer box interlock
solenoid.
A diode is included in the supply line to the solenoid to prevent residual current causing the solenoid to stick in the
energised position.
The transfer box solenoid interlock option can be programmed in one of three states dependent on market/ customer
requirements, these are:
lOption 1– not fitted.
lOption 2 – normal operation.
lOption 3 – inhibit transfer box.
The BCU checks the status of the following inputs to determine the logic action for employing the transfer box interlock
solenoid (transfer box solenoid enable):
lIgnition state.
lGearbox state.