Discovery 2. Manual - part 742

BODY CONTROL UNIT

DESCRIPTION AND OPERATION 86-3-35

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:

l

Ignition state.

l

Perimetric 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.
 

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 INSTRUMENTS, DESCRIPTION AND OPERATION, Description.

Seat belt warning
The BCU can be programmed to include seat belt warning using one of four options:

l

Option 1 – warning on for 6 seconds.

l

Option 2 – warning on for 6 seconds or until the seat belt is fastened.

l

Option 3 – warning on for 6 seconds unless the seat belt is fastened.

l

Option 4 – no warning.

The BCU checks the status of the following inputs:

l

Ignition on.

l

Seat belt fastened.

Depending on the logic conditions of the inputs, the BCU provides the following outputs:

l

Audible warning No.1 requested.

l

Seat 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.

BODY CONTROL UNIT

86-3-36 DESCRIPTION AND OPERATION

Key-in warning
The BCU can be programmed to one of two options:

l

Option 1 – no timeout.

l

Option 2 – no key-in warning.

The BCU issues an audible warning No. 2 request, depending on the status of the following inputs:

l

Ignition state.

l

Ignition key inserted.

l

Driver's door open.

If the key-in warning is programmed into the BCU for operation, audible warning No.2 will be requested if the ignition 
switch is off, the ignition key inserted signal is on and the driver's door open signal is ON.

In the event of a communications link failure occurring, the audible warning request is not sent to the instrument pack.

SLABS HDC warning
The BCU issues an audible warning No. 3 request, depending on the status of the following inputs:

l

Ignition state.

l

SLABS HDC warning.

The SLABS warning transmitted by the SLABS ECU is a 2 Hz signal, audible warning No. 3 is requested on every 
falling edge of this signal. If the signal from the SLABS ECU stays low for more than 650 ms, audible warning No. 3 
is requested every 2 seconds, for 30 seconds, while the signal stays low.

In the event of a communications link failure occurring, the audible warning request is not sent to the instrument pack.

Transfer box in neutral warning
If the transfer box is in the neutral position and the ignition switch is on, the BCU issues an audible warning No. 4 
request. The BCU checks for the following inputs:

l

Transfer box neutral selected.

l

Ignition on.

The transfer box in neutral warning is activated by communicating with the instrument pack via the serial datalink. If 
a communications link failure occurs while the transfer box in neutral warning is active, the audible warning will not 
operate.

Lights on warning
If the ignition switch is off while the side lamps or headlamps on and the driver's door is opened, the BCU issues an 
audible warning No. 5 request.

The BCU checks for the following inputs:

l

Driver's door open.

l

Ignition on.

l

Side lamps.

l

Dipped beam state.

l

Main beam state.

The lights on warning is activated by communicating with the instrument pack via the serial datalink. If a 
communications link failure occurs while the lights on warning is active, the audible warning will not operate.

BODY CONTROL UNIT

DESCRIPTION AND OPERATION 86-3-37

SLABS raise/lower
Before enabling a SLS vehicle raise/ lower request, the BCU checks the logical condition of the following inputs:

l

Ignition state.

l

SLABS raise request.

l

SLABS lower request.

If the ignition switch is in position 0 or I, the vehicle raise/ lower request is off.

With the ignition switch in position II, and the 'SLABS raise' request and 'SLABS lower' request both off, the vehicle 
raise/ lower request output is driven at 25 Hz with a 50% duty cycle and the vehicle height remains unchanged. 

If the 'SLABS lower' request input is on, the vehicle raise/lower request output is driven at 25 Hz with a 25% duty cycle, 
lowering the vehicle. 

If the 'SLABS raise' request input is on, the vehicle raise/lower request output is driven at a 25 Hz with a 75% duty 
cycle.

BODY CONTROL UNIT

86-3-38 DESCRIPTION AND OPERATION