2002 LAND ROVER DISCOVERY relay

BODY CONTROL UNIT
86-3-32 DESCRIPTION AND OPERATION
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.
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.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-33
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.
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.

BODY CONTROL UNIT
86-3-34 DESCRIPTION AND OPERATION
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.
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.

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
DESCRIPTION AND OPERATION 86-4-13
Battery Backed-up Sounder (BBUS)
The BBUS is located behind the rear quarter trim panel on the right hand side of the vehicle and is utilised as an
additional alarm warning device. It has a self contained power source allowing it to operate when the vehicle battery
is disconnected.
NOTE: Always disarm the BBUS before carrying out any procedures related to the BBUS.
Input/Output
The BBUS utilises a 12 volts power supply from fuse 20 (15 amperes) located in the passenger compartment fusebox
via a relay to charge the self contained battery.
When the alarm is triggered, the BCU is pulled high internally triggering the BBUS to sound continuously for 30
seconds.
The BCU sets the BBUS to its internal battery backed mode when the vehicle battery is disconnected.
If a mislock occurs the BCU triggers the BBUS for a period of 50 ms.
The BCU triggers the BBUS once for a period of 50 ms when an EKA code is requested.
When the EKA code is entered correctly, the BBUS will operate twice for a period of 50 ms on, 200 ms off.
The BBUS utilises a dedicated earth path.

ALARM SYSTEM AND HORN
86-4-14 DESCRIPTION AND OPERATION
Vehicle horn/alarm sounder
Vehicle horn
Alarm sounder
Depending on system configuration, the alarm sounder will either sound independently or in conjunction with the
vehicle horns as an alarm triggered warning. The alarm sounder is located under the bonnet on the bulkhead. If the
alarm is triggered, the alarm sounder operates at 0.5 second intervals in phase with the direction indicators.
Input/Output
The BCU provides an earth path for the alarm sounder relay situated in the passenger compartment fuse box.
Fuse 21 supplies battery power to the alarm sounder relay. When an unauthorised entry to the vehicle is detected,
the BCU provides an earth path for the alarm sounder relay. This earth path energises the alarm sounder relay, which
activates the alarm sounder.
If a mislock occurs the BCU triggers the alarm sounder 2 times for a period of 50 ms on, 200 ms off.
The BCU triggers the alarm sounder once for a period of 50 ms when an EKA code is requested.
When the EKA code is entered correctly, the alarm sounder will operate twice for a period of 50 ms on, 200 ms off.
The alarm sounder relay has a dedicated signal to the BCU.

WINDOWS
DESCRIPTION AND OPERATION 86-5-1
WINDOWS DESCRIPTION AND OPERAT ION
Electric windows block diagram
1Passenger compartment fusebox
2BCU
3LH front window switch
4LH front window motor
5RH front window switch
6RH front window motor
7Rear window lift relay8Centre console LH rear window switch
9LH rear door window switch
10LH rear door window motor
11Centre console RH rear window switch
12RH rear door window switch
13RH rear door window motor
14Rear window isolation switch

WINDOWS
DESCRIPTION AND OPERATION 86-5-3
1Passenger compartment fusebox
2Body Control Unit (BCU)
3LH front window switch
4LH front window motor
5RH front window switch
6RH front window motor
7Rear window lift relay
8Centre console LH rear window switch
9LH rear door window switch
10LH rear door window motor
11Centre console RH rear window switch
12RH rear door window switch
13RH rear door window motor
14Rear window isolation switch