Discovery 2. Manual - part 740

BODY CONTROL UNIT

DESCRIPTION AND OPERATION 86-3-27

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:

Ignition state.

RH indicators selected.

LH indicators selected.

Hazards selected.

Inertia switch hazard request.

One short indicator flash request (anti-theft system arming).

Two short indicator flash request (superlocking).

One long indicator flash request (anti-theft system disarming).

Alarm 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:

RH indicators enable.

LH indicators enable.

Direction indicator left message (link to IDM).

Direction 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:

Right direction indicators requested.

Left direction indicators requested.

RH indicators current sense.

LH indicators current sense.

If a direction indicator bulb failure or a trailer presence is detected, the following outputs can be generated depending
on the BCU logic states:

Trailer detected.

Bulb failure detected.

Direction indicator short circuit.

Direction indicator relay stuck.

BODY CONTROL UNIT

86-3-28 DESCRIPTION AND OPERATION

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:

The 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).

The vehicle is unlocked (the hazard warning lamps flash once for a duration of two seconds).

The anti-theft alarm system is triggered (the hazard warning lamps flash in phase with and for the duration of the
audible warning).

The hazard warning switch is pressed (the hazard warning lamps flash until the hazard warning switch is pressed
for a second time).

The 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

Trailer detected

None (bulbs okay)

Bulb failure detected

Direction indicator short circuit detected

BODY CONTROL UNIT

DESCRIPTION AND OPERATION 86-3-29

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:

Ignition state.

Remote locking request.

Remote unlocking request.

Lazy 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:

Option 1– no daylight running lamps.

Option 2 – on with main beam off.

Option 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:

Main beam state.

Engine running (link from instrument pack).

Dipped beam.

Gearbox 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.

BODY CONTROL UNIT

86-3-30 DESCRIPTION AND OPERATION

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.

Front fog lamps
Front fog lamp operation is monitored by the BCU, which allows only the front fog lamps to operate when the side
lamps or headlamps are on. When the side lamps, headlamps or ignition switch is turned off, the BCU also switches
off the fog lamps. When the side or headlamps are switched on again, the front fog lamps will remain off unless the
front fog lamp switch is pressed to resume operation. If the rear fog guard lamps are selected on, switching off the
front fog lamps will also switch off the rear fog guard lamps.

When the fog lamp switch is operated, an earth path is completed and the BCU allows the fog lights to be switched
on providing the logical preconditions have been satisfied. The BCU then supplies a voltage supply to the fog lamp
relay, to illuminate the fog lamps.

The front fog lamps option can be programmed in one of three states dependent on market/ customer requirements,
these are:

Option 1– not fitted.

Option 2 – main beam no effect.

Option 3 – off with main beam.

The BCU checks the status of the following inputs to determine the logic action for providing an output to the front fog
lamp relay:

Ignition state.

Main beam state.

Side lamps.

Dipped beam.

Front fogs selected (press button, not latched).

If the ignition state is crank the state of the front fog relay is memorised and the relay is switched off. Pressing the
front fog switch during cranking will not be recognised. When the ignition state returns to Ignition after cranking, the
memorised front fog relay state is restored. If the ignition is turned off, the front fog relay is turned off.

For option 3 configuration, if the main beam is turned on the state of the front fog relay is memorised and the relay is
switched off. Pressing the front fog switch while main beam is on will not be recognised. When the Main beam state
returns to OFF, the memorised front fog relay state is restored.

In the event of a communications link failure while the front fog relay is on, the front fog relay will be switched off.

Rear fog lamps
The rear fog lamps operation is monitored by the BCU, which only allows the rear fog lamps to operate when the side
lamps or the headlamps are on. When the side lamps, headlamps or ignition is switched off, the rear fog lamps are
also switched off. When the side lamps or headlamps are switched on again, the rear fog lamps will not switch on
again unless reselected by operating the rear fog lamps switch. If front fog lamps are fitted, the rear fog lamps will be
switched off if the front fog lamps are switched off.

A supply voltage to the rear fog lamps relay is provided from a fuse in the passenger compartment fuse box, then
through two electronic switches in the IDM. With the lighting switch in the side lamp or headlamp position, an earth
path from the coil of the rear fog lamps relay completes the circuit through the two switches in the IDM to switch the
rear fog lamps on when the BCU receives a request signal from the rear fog lamps switch to turn the circuit on.

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