Discovery 2. Manual - part 318

BODY CONTROL UNIT

DESCRIPTION AND OPERATION 86-3-13

Anti-theft system
The BCU controls the logical switching operations for enabling and activating the anti-theft system. Features include:

Perimetric protection – monitors the condition of doors and hinged panels.

Volumetric protection – monitors the vehicle's interior space.

Remote locking, superlocking and unlocking functions.

Engine immobilisation and remobilisation.

Advanced mislock detection and automatic compensation.

EKA code functions.

Customer configuration options.

Market configuration options.

Immobilisation
The immobilisation system comprises the following components:

RF receiver.

RF transmitter/ transponder.

Transponder coil.

BCU.

Door switches, door lock switches and bonnet switch.

IDM.

ECM.

Starter solenoid relay.

Status LED.

Alarm system
The alarm system comprises the following components:

RF receiver.

RF transmitter.

BCU.

IDM.

Door switches, door lock switches and bonnet switch.

Battery backed-up sounder (BBUS).

Status LED.

On non NAS vehicles, power supply for the alarm sounder and the battery BBUS is provided through two relays in the
passenger compartment fuse box. Each of the coils of the alarm relays are directly connected to the IDM which
controls their operation under the direction of BCU signals received via the serial data bus.

On NAS vehicles, an audible warning is provided through operation of the vehicle horns. The BCU provides an earth
path for the coil of the horn relay to initiate vehicle horn operation.

ALARM SYSTEM AND HORN, DESCRIPTION AND OPERATION, Description.

Acclimatisation locking

Disabled

The vehicle cannot be locked if the ignition is on.

Enabled

The vehicle can be locked if the ignition is on and the engine is
running.

Alarm tamper

Disabled

The security system LED does not flash when the security system has
been tampered with.

Enabled

The security system LED flashes when the security system has been
tampered with.

Engine immobilised

LED off

The security system LED does not flash when the engine is
immobilised.

LED flash

The security system LED flashes when the engine is immobilised.

Low battery warning

Disabled

The security system LED does not flash when the remote transmitter
battery is low.

Enabled

The security system LED flashes when the remote transmitter battery
is low.

Emergency Key Access
(EKA)

Disabled

EKA is disabled.

Enabled

EKA is enabled and the door locks operate electrically.

No unlock

EKA is enabled, but the door locks do not operate electrically.

Function

Option

Details

BODY CONTROL UNIT

86-3-14 DESCRIPTION AND OPERATION

Central Door Locking (CDL)
The BCU carries out the logic control operation for CDL. A CDL switch is mounted on the fascia panel and has two
inputs to the BCU, one for lock and one for unlock.

Door locking and unlocking can be performed using the remote transmitter in the keys and the receiver unit located
above the vehicle's headlining, behind the rear sunroof aperture. The receiver detects the signals sent from the
remote transmitter and sends a decoded signal to the BCU for processing.

Four methods of door locking are available:

Remote handset locking.

Vehicle key locking.

CDL switch locking.

Speed related locking.

Two security levels of door locking are available, CDL and Superlocking. The anti-theft alarm system works in
conjunction with the CDL system.

Electric windows and sunroof
The BCU controls the logical operations and the timing periods for the electric front windows. The rear windows are
hard-wired and the two electric sunroofs are controlled by a dedicated ECU which is enabled by the BCU.

The front windows are electrically operated using two rocker switches located in the centre console. Electric motors
are located in each of the front doors.

The rear windows are enabled by the IDM controlling the operation of the rear window relay located in the passenger
compartment fuse box.

Wipers and washers
The wiper and washer functions are controlled by the BCU and the IDM.

The front wipers and washers are operated from the switch stalk located on the right hand side of the steering column
and only operate when the ignition switch is in position I or II. The front wipers are operated by a motor located below
the windscreen plenum.

WIPERS AND WASHERS, DESCRIPTION AND OPERATION, Description.

The BCU controls the wiper motor frequency of operation via the IDM when intermittent wipe or wash is selected. The
front intermittent wipe option features five different intermittent delay periods. The shortest delay period is 3 seconds
and this is increased by 2 second increments up to a maximum delay of 11 seconds. The desired delay period for the
front wipers is set by the position of the rotary switch located on the wiper column stalk.

The rear wiper switch is located on the instrument pack cowl and is latched when pressed. The rear wiper electric
motor is located in the tail door. The rear wiper operation is controlled according to a programmed strategy via the
BCU and the IDM. The BCU also checks for a signal from either the reverse lamp switch located in the vehicle gearbox
(manual gearbox models) or the gear position switch (automatic gearbox models) for operating the rear wipers when
the vehicle is in reverse. The rear wiper and washer only operate when the ignition switch is in position II.

The front and rear washer pumps and the headlamp powerwash (where fitted) are also controlled through the BCU.
The washers are operated from electric pumps attached to the washer reservoir located in the left hand wheel arch.
The front wash switch is located on the wiper column stalk and is pulled towards the steering wheel to select the
washer function. When the front washers are operated, the wipers are also activated for three full cycles. The rear
wash switch is located on the instrument pack cowl. The BCU programme can be configured in one of two modes of
operation:

No wiper operation when the wash switch is pressed.

Wiper action after an initial delay of 400 ms.

Headlamp wash is activated by the BCU via the IDM and operates when the headlamps are on and the front washers
function is selected.

BODY CONTROL UNIT

DESCRIPTION AND OPERATION 86-3-15

Electric seats
The BCU controls the logical operation of the electrically operated front seats. Two modes of operation are available:

SEATS, DESCRIPTION AND OPERATION, Description - electric seats.

Electric seat adjustment is enabled if the ignition is on or the driver's door is opened for a short time period.

Electric seat adjustment is enabled if the ignition is on and the driver's door is closed.

The seats are operated by four electric motors which control the seat cushion rear up/ down, the seat cushion front
up/ down, seat cushion forward/ rearward and seat squab recline. The electrically powered lumbar adjustment in each
seat is operated by a single motorised air pump and a solenoid located on the seat squab frame. The air pump inflates
a cushion in the seat squab and the solenoid operates a valve to deflate the cushion. The seat squab and cushion
may also contain heater elements to provide heated seat operation.

The switches for electrically operated seats are located either side of the centre console.

Direction indicators and hazard warning lamps
The direction indicator lamps are operated from a three position direction indicator switch on the left hand, steering
column stalk. The BCU only allows the lamps to work as direction indicators when the ignition switch is in position II.
The BCU also controls the lamps to operate as hazard warning lamps and as a visual warning for the anti-theft system,
in which cases all lamps flash simultaneously irrespective of the ignition switch position.

System control of the direction indicators and hazard warning lamps is provided by the BCU operating with the IDM
and two electronic relays located in the passenger compartment fuse box. The IDM and relays are integral parts of
the passenger compartment fuse box and cannot be serviced individually. The serial data bus is used for
communication of status and operation requests between the BCU, IDM and instrument pack.

The hazard warning lamps are operated from a latching pushbutton switch located on the fascia.

All direction indicator/ hazard warning lamp bulbs are rated at 5 Watts.

Headlamps
The BCU contains a feature which allow the vehicle headlamps to be turned on when the remote transmitter is
pressed (courtesy headlamps).

For markets with daylight running lamps, the BCU controls the logical operation of the daylight running lamps. Options
are daylight running lamps are on if the main beam headlamps are off, or the daylight running lamps are on with main
and dipped beam off and the gearbox not in Park.

Front fog lamps
For markets with front fog lamps fitted, the BCU controls the operation of the front fog lamps. Options can be selected
so that the fog lamps will operate with or without the headlamps on main beam.

Instrument pack
The BCU communicates with the instrument pack via a serial data bus.

INSTRUMENTS, DESCRIPTION AND OPERATION, Description.

The instrument pack provides the BCU and IDM with details of vehicle speed.

Signals are provided from the IDM to the instrument pack and BCU when the direction indicator lamps are active.

For certain markets, the BCU provides a signal to the instrument pack for indicating when the transfer box is in
neutral.

The IDM can signal the instrument pack to illuminate a trailer warning lamp. This operates when the IDM senses
that the current drawn by the indicator circuit exceeds a preset threshold.

The odometer reading displayed on the instrument pack LCD screen is also stored in non volatile memory in the
BCU. Whenever the ignition is turned from position I to position II, the instrument pack and the BCU compare
their stored values.

The gear selector position is displayed on the instrument pack LCD screen under the direction of the BCU.

Starting
The starting system comprises a starter motor and solenoid located at the rear right hand side of the engine. A starter
relay controlled by the BCU is used to supply battery power for starter solenoid operation. The starter motor receives
its feed directly from the battery.

BODY CONTROL UNIT

86-3-16 DESCRIPTION AND OPERATION

Cruise control
The BCU processes several signals used for cruise control:

When the brake pedal is pressed, a low voltage brake lamp signal is sent via the BCU to the cruise control ECU.

The gear position switch sends an input via the BCU to the cruise control ECU if the selector lever is in Park,
Neutral or Reverse.

A voltage supply is fed from the BCU to the cruise control SET+ switch.

A voltage supply is fed from the BCU to the cruise control RES switch.

On vehicles with automatic transmission, if the BCU receives an input from the gear position switch or the brake pedal
switch, the BCU sends a signal to the cruise control ECU to cancel or inhibit cruise control operation.

ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.

ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - cruise control.

Shift interlock (where fitted)
On automatic gearbox models, the BCU and IDM combine with an interlock relay located in the passenger
compartment fuse box to operate a shift interlock solenoid, so that the gear selector lever cannot be moved out of
Park until 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.

Ignition key interlock (where fitted)
On automatic gearbox models, the ignition key interlock solenoid prevents removal of the ignition key from the ignition
switch when the transmission gear selector is not in the Park position. The logic control operation for this is performed
by the BCU.

Transfer box interlock (where fitted)
On automatic gearbox models, a transfer box interlock solenoid is controlled by the IDM to prevent transfer box shift
lever being moved out of high or low range unless certain conditions have been satisfied. The IDM controls the
operation of the transfer box relay which is located in the passenger compartment fuse box.

TRANSFER BOX - LT230SE, DESCRIPTION AND OPERATION, Description.

Gear position switch
A gear position switch is located on the automatic gearbox and is used to inform the BCU of the gear selector lever
position. The BCU has four sensing inputs from the gear position switch contacts W, X, Y, Z, which are used to
determine the gearbox drive status at any particular instance. The BCU gives an output corresponding to the gearbox
status derived from the gear position switch inputs. The logic states defining the gear selector positions are listed in
the table below, where Z1, Z2, Z3 and Z4 represent intermediate states which exist as the selector lever position is
changed:

Gear position

Switch contacts

P (Park)

R (Reverse)

N (Neutral)

D (Drive)

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