ESP LAND ROVER DISCOVERY 1999 Repair Manual

BODY CONTROL UNIT
86-3-16 DESCRIPTION AND OPERATION
Cruise control
The BCU processes several signals used for cruise control:
lWhen the brake pedal is pressed, a low voltage brake lamp signal is sent via the BCU to the cruise control ECU.
lThe gear position switch sends an input via the BCU to the cruise control ECU if the selector lever is in Park,
Neutral or Reverse.
lA voltage supply is fed from the BCU to the cruise control SET+ switch.
lA 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
WX Y Z
P (Park) 1 0 0 0
Z11100
R (Reverse) 0 1 0 0
Z11100
N (Neutral) 1 1 1 0
Z21010
D (Drive) 1 0 1 1
Z31111
30111
Z40011
20001
Z40011
10010

BODY CONTROL UNIT
86-3-18 DESCRIPTION AND OPERATION
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
2Key-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 86-3-27
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
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.

ALARM SYSTEM AND HORN
DESCRIPTION AND OPERATION 86-4-21
Passive immobilisation
Passive immobilisation prevents the vehicle from being started unless the authorised key is used to start the vehicle.
There are only two configurations for passive immobilisation:
lpassive immobilisation not active
lpassive immobilisation active
When the ignition is switched off, the vehicle remains mobilised for up to a maximum of 5 minutes. If however the
driver's door is opened, after 2 minutes 30 seconds, the vehicle remains in a mobilised state for a further 30 seconds.
When the timer in the BCU has expired, the vehicle is immobilised.
Once the ignition is switched on, the BCU transmits a coded signal to the ECM. If the coded signal does not
correspond to the programmed code in the ECM, the ECM is inhibited and the BCU inhibits the starting circuit.
In order for passive immobilisation to occur, the following conditions must be met:
lDriver's door closed.
lFuel cut-off switch not tripped.
lKey not inserted in ignition.
Passive remobilisation
Whenever the vehicle is immobilised, passive remobilisation of the engine occurs when the ignition is switched on,
allowing the vehicle to be started.
There are three configurations for passive remobilisation:
lPassive immobilisation not active.
lPassive immobilisation active.
lEKA with super locking on receiving good passive remobilisation exciter coil signal.
The BCU controls the passive remobilisation exciter coil (located around the ignition barrel) to generate a magnetic
field which causes the handset to transmit a remobilisation signal. The BCU receives the signal and allows the vehicle
to be started. If a valid signal from the handset is not received within one minute of the ignition being switched to
position II, the BCU stops the passive coil from generating the magnetic field.
Emergency key access
If the handset fails to operate, the engine can be remobilised by using the key to enter a unique four digit Emergency
Key Access (EKA) code.
There are three configurations for emergency key access:
lEKA not active (no immobiliser fitted).
lEKA active.
lEKA with super locking on receiving good passive remobilisation exciter coil signal.

DRIVING AIDS
86-8-8 DESCRIPTION AND OPERATION
Sensors
Four sensors are positioned in the rear bumper. Each sensor comprises an outer housing with an angled rubber trim
which differs between the inner and outer sensors and the sensor body. The outer housing has a slot which engages
with a pin on the sensor body and is locked by rotating the sensor. A coil spring around the sensor is compressed
when the sensor is installed in the bumper and maintains the sensor housing engaged on the pin. The sensor housing
has a raised lip at the top which locates in a corresponding groove in the bumper mounting hole and sets the correct
orientation for the sensor body.
Each sensor has a three pin connector which connects into a common harness linking all four sensors. This harness
is connected to the main vehicle body harness. The three pins are for sensor negative and positive feeds and a signal
line.
Each sensor comprises a plastic housing which contains a piezoelectric disc. The disc resonates at a frequency of
38.4kHz, producing an ultrasonic signal output. The disc also receives the reflected echo signal.
The PDC ECU controls the operating mode of each sensor by output of a digital signal on the signal line. Each sensor
has two modes of operation; combined transmitter and receiver mode or receiver mode only.

NAVIGATION SYSTEM
87-22 DESCRIPTION AND OPERATION
On-Board Monitor (Display Unit)
Selecting ON-BOARD MONITOR from the service mode menu displays the version information for the display unit.
Version Information Menu
Selecting Functions, on the on-board monitor (display unit) version information menu, brings up a functions menu.
From the functions menu, the operation of the control switches can be checked and the brightness of the LCD can be
adjusted.
Control Switch Check
Selecting Key Function on the display unit functions menu brings up a menu with three items:
lKey – This item allows the operation of the push switches to be checked. While a switch is pressed, a
corresponding value is shown. The values for the push switches are as follows:
l01 – Mute switch
l02 – Re-Rte switch
l03 – Menu switch
l04 – Repeat switch
l05 – Rotary controller pushed
lFE – Multiple switches pushed
lFF – No switch pushed
lOBM increment sensor – This item allows the rotary operation of the rotary controller to be checked. The value
should decrease when the rotary controller is turned clockwise and increase when the rotary controller is turned
anti-clockwise
lRadio increment sensor - No value for this item will register on the Discovery II system.
If there are no inputs on the switch pack for 3 seconds, the Functions item becomes active. Selecting returns the system to the service mode menu.
M86 6067
On Board Monitor Version
SW LEVEL
HW LEVEL
DIAG LEVEL
BUS INDEX
ENCODING INDEX
SUPPLIER
< Return25
20
11
07
00
16
Functions

INSTRUMENTS
DESCRIPTION AND OPERATION 88-7
LCD odometer/trip meter
The LCD has 3 different display elements:
lOdometer.
lTrip meter.
lSelected gear (on vehicles with automatic gearboxes).
The odometer displays units in either miles or kilometres. It has a range from 0 to 999,999 units, only full units are
displayed irrespective of the type of units selected, the display will stop at 999,999 units. TestBook can be used to
reset the odometer. This is allowed only once and must be carried out before 150 miles (240 km) from new, after this
distance the feature is disabled. The odometer may lose up to one km (0.6 miles) when the battery is reconnected,
this is due to the software incorporated into the instrument pack to prevent anyone tampering with the odometer
reading.
The trip meter displays units in either miles or kilometres and has a range of 0.0 to 999.9 units. The display rolls over
from 999.9 to 0.0 units. Units down to one tenth of a mile or one tenth of a kilometre are displayed. The trip meter
displays 0.0 when the battery is reconnected or charged from a discharged state.
A push button located next to the LCD is utilised to reset the trip meter to zero and to change the units from miles to
kilometres. Pressing the button for less than 2 seconds allows the display to reset to zero. Pressing the button for
more than 2 seconds changes the units from miles to kilometres and vice versa. The units will only change for UK,
NAS and Canadian market vehicles.
The selected gear displays when the automatic gearbox is in park, reverse, neutral, drive 3,2,1, by using the letters
or numbers PRND321 in the display.
The data input for the LCD odometer/trip meter is from the SLABS ECU for the distance input and from the BCU for
the gear position. The instrument pack provides the earth path to illuminate the gear position warning lamp.
If a replacement instrument pack is required TestBook must be used to retrieve the odometer reading, so that when
the new instrument pack is fitted the odometer reading can be programmed in.

INSTRUMENTS
DESCRIPTION AND OPERATION 88-19
High engine coolant temperature warning lamp
The high engine coolant temperature warning lamp within the instrument pack utilises a red LED and a clear legend.
The ECM illuminates the LED when it detects the engine coolant has exceeded a temperature of 121 °C (250 °F) and
switches it off when the coolant temperature drops below 118 °C (244 °F). The ECM also illuminates the high engine
coolant temperature warning lamp when it detects the PWM duty cycle to the temperature gauge is out of range. If it
is greater than 94% duty cycle when the engine is hot, or less than 8% duty cycle when the engine is cold, the engine
coolant temperature gauge pointer will indicate cold, thus alerting the driver with an additional visible warning.
When the ignition is switched on, the ECM illuminates the LED to provide a self-check, providing there is no fault it
will remain illuminated for 3 seconds or until the ignition is switched off.
The response of the engine high temperature warning lamp varies according to engine type and market, there are
three conditions:
lV8 - Gulf.
lV8 - all markets except Gulf.
lDiesel - all markets.
The vehicle configuration determines which condition is set.
The PWM duty cycle thresholds for illuminating and extinguishing the warning lamp are given in the table below.
The power input for the LED is supplied by the instrument pack via fuse 27. The ECM controls the earth path to
illuminate the warning lamp.
Market Lamp on Lamp off
V8 - Gulf 79.8 ± 2% 77.8 ± 2%
V8 - all markets except Gulf 77.8 ± 2% 75.7 ± 2%
Diesel - all markets 78.8 ± 2% 76.8 ± 2%

INSTRUMENTS
DESCRIPTION AND OPERATION 88-33
Engine oil pressure warning lamp
The engine oil pressure warning lamp within the instrument pack utilises a red LED and a clear legend. The LED
illuminates when the engine oil pressure is below the specified pressure (see table), providing the driver with a visible
warning that the engine oil pressure has fallen below the specified minimum reading.
There is no self-test performed at ignition on for this warning lamp.
The power input for the LED is supplied by the instrument pack via fuse 27. The oil pressure switch located on the
engine provides the earth path to illuminate the warning lamp, it will remain illuminated until the engine is started and
the oil pressure exceeds the appropriate threshold and opens the switch contacts.
Low oil pressure switch operating pressures
The response to the voltage signal at the instrument pack is as follows:
l< 1.8 volts = warning lamp on.
l> 7.7 volts = warning lamp off.
Engine type Switch opening pressure, bar (lbf.in2)
V8 0.22 to 0.59 (3.0 to 8.5)
Diesel 0.25 to 0.42 (3.5 to 6.0)