1999 LAND ROVER DISCOVERY fuel

AIR CONDITIONING
DESCRIPTION AND OPERATION 82-13
The control panel switches are all non-latching pushswitches except for the LH and RH temperature switches, which
are centre-off rocker switches. The switches have the following functions:
LH and RH temperature switches. Enabled only while the system is on:
lEach press increases or decreases the related temperature setting, in steps of 1 °C (2 °F), between 16 and 28
°C (60 and 84 °F).
lIf the decrease side of the switch is pressed when a temperature of 16 °C (60 °F) is set, the display changes to
LO (maximum cold).
lIf the increase side of the switch is pressed when a temperature of 28 °C (84 °F) is set, the display changes to
HI (maximum hot).
lIf a switch is kept depressed, step changes occur every 0.4 seconds.
A/C on/off switch. Switches the system on and off. When used to switch the system on, the system resumes the
configuration in use prior to the previous off selection.
Blower switch. Enabled only while the system is on. Provides manual control of blower speed:
lEach press changes the blower speed, in sequence, through off (only available if economy mode is selected on)
and five incremental speeds.
lIf the switch is kept depressed, after 1 second subsequent speed increments occur every 0.4 second until blower
reaches high speed. Releasing and then pressing the switch again changes blower back to off or low speed.
Distribution switch. Enabled only while the system is on. Provides manual control of air distribution:
lEach press changes the air distribution, in sequence, through footwells only, footwells and windscreen/side
windows demist, windscreen/side windows demist only, face level only, face level and footwells.
lIf the switch is kept depressed, after 1 second subsequent distribution changes occur every 0.4 seconds until
distribution reaches face level and footwells. Releasing and then pressing the switch again changes distribution
back to footwells only.
External air temperature (EXT) switch. Enabled while the system is on or off. Switches the external temperature output
on and off:
lIf the system is already on, the temperature output overrides the system outputs for approximately 7 seconds,
then the display reverts to system outputs.
lIf the system is switched on while the external temperature output is on, the system outputs override the external
temperature output.
Fresh/Recirculated air switch. Enabled only while the system is on. Provides manual control of inlet air selection.
Defrost mode switch. Starts the system in, or switches the system to and from, defrost mode.
Automatic mode (AUTO) switch. Starts the system in, or switches the system to and from, the automatic mode.
Economy mode (ECON) switch. Enabled only while the system is on. Provides manual on/off control of the refrigerant
system compressor, to reduce fuel consumption when there is no requirement for cool or dehumidified air, e.g. when
the ambient temperature is lower than the LH and RH temperature settings.
Temperature settings: The LH and RH temperature settings are reference inputs used by the control system and give
an approximation of the temperatures that will be established in the cabin. They are not necessarily actual distribution
outlet temperatures, or the temperatures at specific points in the cabin.
Audible warning: A 'beep' is emitted from the ATC ECU each time it receives a control switch input. This audible
warning can be switched off and on by pressing and holding the AUTO switch, then pressing and holding the A/C on/
off switch until the audible warning sounds (approximately 3 seconds). While switched off, the audible warning still
sounds when:
lSwitching between °F and °C on the display.
lSwitching the audible warning from off to on.
lSwitching the timed feet function on and off.
lSwitching the timed recirculated inlet air on and off.
lSwitching the latched recirculated inlet air on and off.
lWhen there is a fault warning.
lRunning the self diagnostic routine.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-1
BODY CONTROL UNIT DESCRIPTION AND OPERAT ION
Description
General
The Body Control Unit (BCU) is located behind the passenger glovebox and is connected to the main harness by four
connectors on its bottom edge and an additional connector located on the side of the BCU casing. Mounting the BCU
behind the fascia makes it reasonably inaccessible for intruders to disable the anti-theft system.
The BCU uses solid-state microprocessor control to perform logical operations and timing functions for a variety of
the vehicle's electrically operated systems, these include:
lDoor locking.
lAnti-theft alarm and immobilisation system.
lExterior lighting including direction indicators and hazard warning lamps.
lCourtesy lighting.
lWipers and washers.
lElectric windows and sunroof.
lHeated windows.
The BCU also communicates with several other electronically controlled systems such as the EAT ECU and SLABS
ECU and also has a datalink between the Intelligent Driver Module (IDM) and the instrument pack. The datalink is a
low speed bus capable of transmitting and receiving messages at a data rate of 10,400 bits per second. Additional
inputs and outputs to peripheral devices are included which are necessary for determining vehicle status for particular
logical operations e.g. crank, ignition key inserted, fuel flap enable etc.
The BCU receives its power supply from the engine compartment fuse box, and is protected by a 10 A fuse.
The BCU communicates with the IDM to provide the control signals to perform power switching operations in
conjunction with dedicated relays.
IDM
The IDM is integrated into the passenger compartment fuse box, which is mounted behind the fascia below the
steering column. There are no harnesses between the fuse box and the IDM. The IDM performs the power switching
operations for several of the vehicle's electrical systems.
The IDM communicates with the BCU and the instrument pack via a serial interface. If the BCU or the IDM is replaced,
the communications link between the two units has to be re-established. This can be done either by switching on the
ignition and leaving it on for five minutes, or by using TestBook. The vehicle immobilisation will remain active until the
communications link between the BCU and IDM has been re-established.
Transit mode
To prevent excessive battery drain during transit to overseas markets, the vehicle is placed in a transit mode. The
following functions are disabled when the vehicle is in transit mode:
lVolumetric sensors.
lPassive immobilisation.
lImmobilisation of the vehicle by use of door lock.
lIgnition key interlock.
lElectric seat enable time-out with driver's door open.

BODY CONTROL UNIT
86-3-2 DESCRIPTION AND OPERATION
Power supply
Battery supply to the BCU and the IDM is provided through a 10 A fuse located in the engine compartment fuse box.
The BCU unit receives an ignition switched power supply (ignition switch position II) input via a 10 A fuse in the
passenger compartment fuse box.
The BCU receives a signal when the ignition switch is turned to the crank position, it then supplies an earth path to
the starter relay coil, to enable the crank operation by supplying power through the starter relay contacts to the starter
motor.
Battery voltage is monitored and BCU operation will function normally between 8 and 18 volts. Between 5.7 and 8
volts the BCU is in the 'under volts' state. The status of the battery is used to determine which outputs may be driven.
If a voltage supply above 18 volts is experienced, outputs will not normally be driven except for those functions which
are required during cranking (robust immobilisation, antenna coil, crank enable relay and feed to gear position switch
contacts W, X, Y, Z). In the over voltage state the vehicle can be driven, but all other functions are disabled and
outputs are switched off (power windows, heated screen, direction indicators etc.).
All functions are disabled on power up until communications between the BCU and IDM have been established. If
communications cannot be established, operation will commence with degraded functionality.
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:
lDoor latch switches.
lDriver's door key lock/ unlock switches.
lBonnet activated security system.
lVolumetric sensors.
lCentral Door Locking (CDL) switches.
lRemote transmitter (via receiver unit).
lInertia fuel cut-off switch.
lIgnition switch.
lFuel flap release switch.
The input voltages (V
in) for BCU digital signals are defined as follows:
lLogic 1 when V
in ≥ 6V.
lLogic 0 when V
in ≤ 2V.
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.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-3
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:
lInterior courtesy lamps.
lFuel flap release actuator.
lAnti-theft status LED.
lEngine Control Module.
lDoor lock actuators.
lDirection indicators and hazard warning lamps.
lHeadlamps.
lAlarm sounder.
lVehicle horns.
lBattery backed sounder.
lStarter relay.
lPassive 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.
BCU to harness connectors
1Connector C0661
2Connector C0662
3Connector C06634Connector C0660
5Connector C0664
The pinout details for the BCU connectors are defined below:

BODY CONTROL UNIT
86-3-8 DESCRIPTION AND OPERATION
C0664 connector pin details
IDM inputs
The IDM inputs are communicated to the BCU using the serial datalink so that the BCU can perform the necessary
logic operations:
The V
in for IDM digital signals are defined as follows:
lLogic 1 when V
in ≥ 8V.
lLogic 0 when V
in ≤ 2V.
IDM input voltages between 2 and 8 volts are indeterminate and cannot be guaranteed.
Pin No. Description Input/Output
1 Front left window down Output
2 Front right window down Output
3 Fuel flap release Output
4 Front left window up Output
5Earth -
6 Front right window up Output
7 Battery power supply Input
Description Signal type System
Inertia switch Digital Locking/ Unlocking/ Alarm
Side lamps Digital Exterior lighting
Headlamp dipped beam Digital Exterior lighting
Headlamp main beam daylight running lamps Analogue Exterior lighting
RH direction indicators current sense Analogue Direction indicators/ Hazards/ Alarm
LH direction indicators current sense Analogue Direction indicators/ Hazards/ Alarm
Front wiper park sense Digital Wipers and washers

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-17
The existence of an intermediate state causes a fault code to be detected by the BCU. To reduce the chances of the
fault condition occurring while changing selector lever position, the inputs are debounced and only considered valid
when they have existed for at least 33 ms.
Transmission neutral selector
The transmission neutral sensor provides an earth signal to the BCU when the transfer box is in neutral. The earth
signal causes the BCU to operate an audible warning when the transfer box is in neutral with the ignition switched on.

+ TRANSFER BOX - LT230SE, DESCRIPTION AND OPERATION, Description.
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 on vehicles up to 2003 model year or in the instrument pack binacle on vehicles from
2003 model year. The switch receives a voltage supply from the passenger compartment fuse box.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-19
Operation
For IDM inputs which are also inputs for BCU functions, the delay before the BCU recognises the change in input
status is less than 250 ms. The BCU uses a debounce algorithm to ignore changes in input having a duration less
than 100 ms with the exception of automatic gearbox W, X, Y, Z inputs, which have a debounce period of 33 ms.
Transit mode
To prevent excessive battery drain during transit to overseas markets, the vehicle is placed in a transit mode.
To exit the transit mode, simultaneously hold down the heated rear window switch and the rear fog lamp switch, turn
the ignition switch from 0 to II and, after a minimum of 2 seconds, release the switches.
Transit mode can be entered using TestBook. When TestBook communicates with the BCU for diagnostics related to
BCU operation, it first checks that the vehicle is not in transit mode.
Anti-theft system
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.

+ ALARM SYSTEM AND HORN, DESCRIPTION AND OPERATION, Description.
Immobilisation
For immobilisation, the BCU disables the starter motor relay. When the engine is cranking, the ECM looks for a coded
signal from the BCU. If the signal is not received within one second of cranking, the fuel supply to the engine is
stopped and the injectors are disabled. This also prevents unburnt fuel from entering the catalyst.
If the BCU is disconnected, the engine starter motor will remain isolated by the starter motor relay and the ECM will
remain immobilised. The main wiring for the system is contained within the main harness which is relatively
inaccessible, so preventing intruders from disabling the system by cutting the wires for the immobilisation system.
Once the immobiliser has been activated, destruction of the trigger device or the wiring to it will not disarm the system.
The RF transmitter communicates to the BCU via the RF receiver using a 70 bit code. Pressing the unlock button on
the transmitter will re-mobilise the vehicle. The RF transponder is integrated into the metal key assembly, inserting
the key into the ignition switch will induce a signal in the exciter coil to re-mobilise the vehicle.
Anti-theft alarm
The alarm system provides a warning of unauthorised access to the vehicle and includes perimetric and volumetric
monitoring under the control of the BCU.
The perimetric protection system detects opening of all doors, tail door and bonnet and will also detect the operation
of the ignition key switch. The following conditions must be satisfied before the BCU will operate all of the functions
of perimetric protection:
lAll doors and hinged panels are in the closed position.
lIgnition key out of the ignition switch.
lInertia switch is not tripped.
If all conditions are not satisfied the BCU will enter a mislock condition.
The volumetric sensor uses two ultrasonic sensors mounted in the headlining to detect movement within the vehicle.
The alarm will trigger when the sensor signals the BCU for 200 ms or greater. Within a single setting period the alarm
system will allow a maximum of 10 triggers as a result of any combination of sensor inputs. It is possible to lock the
vehicle without enabling the volumetric alarm by using the key. The same conditions needed to satisfy enabling of the
perimetric protection system is also needed to enable volumetric protection.
When the alarm system is set the BCU checks the status of all the inputs from the door and bonnet switches to ensure
the integrity of the vehicle before setting the alarm system into operational mode. In some markets, when the alarm
is set the BCU sends a signal to the IDM which will cause the direction indicators to flash three times for a duration of
3 seconds.
If the sensors are triggered the BCU will activate an alarm sounder to provide an audible warning of a theft attempt.
The activation period of the alarm sounder is 25 to 30 seconds. The duty cycle of the alarm sounder is 50:50 ± 10%.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-33
In the event of a communications link failure occurring while the transfer box enable is on, the output will be switched
off.
Gear position switch
On automatic gearbox models, the BCU provides an output which supplies power to the automatic gearbox gear
position switch. The BCU checks for the following inputs before it supplies power:
lIgnition on.
lAuxiliary.
When the ignition is on, the feed to the gear position switch is on. When the ignition is off and auxiliary is off for more
than 30 seconds, feed to the gear position switch is off.

+ AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Description.
Fuel flap release
The fuel flap release solenoid only operates when the ignition switch is switched off, the anti-theft system is not
activated and the fuel flap release switch is pressed. If the BCU detects that these conditions have been satisfied, it
provides a path to earth for the fuel flap solenoid, so allowing the fuel flap to be opened.
To decide the correct conditions for providing a fuel flap enable output, the BCU checks the following input conditions:
lIgnition state.
lPerimetric alarm state.
If the battery state is not normal, the electric fuel flap enable is switched off.
Audible warnings
The BCU can request the instrument pack to generate an audible warning in response to logic conditions which have
been detected by the BCU and which need to be drawn to the driver's attention.

+ INSTRUMENTS, DESCRIPTION AND OPERATION, Description.
Seat belt warning
The BCU can be programmed to include seat belt warning using one of four options:
lOption 1 – warning on for 6 seconds.
lOption 2 – warning on for 6 seconds or until the seat belt is fastened.
lOption 3 – warning on for 6 seconds unless the seat belt is fastened.
lOption 4 – no warning.
The BCU checks the status of the following inputs:
lIgnition on.
lSeat belt fastened.
Depending on the logic conditions of the inputs, the BCU provides the following outputs:
lAudible warning No.1 requested.
lSeat belt not fastened warning on instrument pack (via datalink to the instrument pack).
When programmed for option 1 operation, audible warning No. 1 is requested when the ignition switch is turned from
off to position II. The audible warning remains active for 6 seconds and a warning lamp on the instrument pack is
illuminated for the same duration.
When programmed for option 2 operation, audible warning No. 1 is requested when the ignition switch is turned from
off to position II. The audible warning remains active for 6 seconds or until the seat belt fastened signal is on and a
warning lamp on the instrument pack is illuminated for the same duration.
When programmed for option 3 operation, audible warning No. 1 is requested when the ignition switch is turned from
off to position II. The audible warning remains active for 6 seconds if the seat belt fastened signal is off; a warning
lamp on the instrument pack is illuminated for the same duration.
In the event of a communications link failure occurring, the audible and visual warning requests are not sent to the
instrument pack.