Range Rover P38 - Electrical System Description and Operation
86
ELECTRICAL
NEW RANGE ROVER
14
DESCRIPTION AND OPERATION
Front and Rear Windows and Sunroof ’Inch Mode’
Function
Operation of any aperture switch for more than 0.4
seconds will cause that aperture to move in inch mode
of operation. The aperture will move in the selected
direction until the motor stalls or the switch is released
or, if the aperture is closing, a trap is detected. The
aperture can be stopped in any position by releasing
the applicable switch.
Windows and Sunroof Anti-Trap Function
The anti-trap function is capable of detecting a trap
situation over the full range of the aperture opening.
When the BeCM detects a trap situation when the
aperture is closing:
- the rear window will open approximately 200 mm
(7.8 in) or until the motor stalls
- the front windows will open fully to the motor stall
position
- the sunroof will open fully to the motor stall
position in the tilt and slide operation.
Anti-trap is sensed by two Hall effect sensors located
within each window and sunroof motor. The sensors
output pulses to the BeCM at a frequency of 62.5 Hz.
When a trap condition occurs, the frequency of the
pulses is reduced and sensed by the BeCM, which
immediately backs off the affected aperture.
Anti-trap override
In extreme temperature conditions the window
mechanism may become partly frozen causing the
window anti-trap function to operate. Anti-trap can be
overridden by operating the window switch in the up
position within 10 seconds of the window having
detected the trap situation and backing off. The
window up function will only operate in inch mode and
the anti-trap override will only continue for along as
the switch is depressed.
Anti-trap override is displayed in the message centre
by an ’ANTI TRAP OFF’ message and the applicable
window denoted. Three audible warning chimes will
sound and will be repeated continuously while the
window is operated with anti-trap override active.
Anti-trap override is only available from the window
control switches in the centre console.
Main Lighting System
The main lighting system is operated by a latching
rotary switch located on the fascia. Movement of the
switch to the side/parking lamps or headlamps
position completes an earth path to the BeCM. When
the switch is in the side lamp position, the earth path
is completed on one of two pins to the BeCM.
When the switch is moved to the headlamp position,
the earth path is completed on both pins. The BeCM
interprets the earth path as request for side or
headlamps and provides power outputs to the
applicable circuits to operate the lamps as requested.
The BeCM outputs are driven by Field Effect
Transistors (FET). The FET’s detect the continuity of
the lighting circuits. In the event of a bulb failure or a
short or open circuit, the break in continuity in that
circuit is sensed by the BeCM which then generates a
’BULB FAILURE’ message in the message centre
specifying the bulb which has failed.
When an FET detects a break in continuity, the output
from the BeCM to the affected circuit is deactivated.
When the fault is corrected, the lighting switch must
be switched off and then on again to reinstate the
output. On certain circuits, the output will be reinstated
by the BeCM automatically.
The number plate lamp circuit is internally linked
inside the BeCM to the glove box lamp circuit. If a
number plate circuit failure occurs, it is advisable to
check the glove box circuit at the same time.
To maximise battery voltage during engine cranking,
most BeCM controlled functions are inhibited. During
cranking, only the side lamps will remain on
irrespective of lighting systems active at the time of
cranking.
Parking Lamps
The parking lamps are located in the tail lamps and
the headlamps. On NAS vehicles the front parking
lamps are located in the front direction indicator lamp
assemblies.