Range Rover P38
86
ELECTRICAL
NEW RANGE ROVER
24
DESCRIPTION AND OPERATION
Supplementary Restraint System DCU
The BeCM communicates with the SRS DCU via
hardwired connections. The BeCM provides a
secondary ignition feed output to the engine
compartment fusebox. When the ignition switch is in
position II, the BeCM provides an output which
generates an ignition supply to the SRS DCU from the
engine compartment fusebox.
See
SUPPLEMENTARY RESTRAINT SYSTEM,
Description and operation.
Cruise Control ECU
The BeCM communicates with the cruise control ECU
via hardwired connections. The BeCM provides a 12
V square wave speed signal input to the cruise control
ECU. The speed signal is derived from the ABS ECU.
The BeCM also supplies a power input to the cruise
control ECU for actuator power. This is supplied via
the normally closed brake switch located in series
between the BeCM and the ECU. When the switch is
closed the BeCM provides a 12 V supply for actuator
power.
When the brake pedal is depressed the switch opens,
pulling the supply low and removing the power supply.
The ECU responds by cancelling cruise control and
opens a dump valve releasing all air stored in the
vacuum system.
See FUEL SYSTEM, CRUISE
CONTROL, Description and operation.
Heating, Ventilation and Air Conditioning (HEVAC)
ECU
The BeCM communicates with the HEVAC ECU via
hardwired connections. The BeCM provides a 12 V
square wave speed signal input to the HEVAC ECU.
The speed signal is derived from the ABS ECU and is
used to control the fan speed.
The BeCM also outputs an alternator signal to inform
the HEVAC ECU that the engine is running and air
conditioning can be operated. Two further outputs are
transmitted to the HEVAC ECU for ignition positions I
and II.
The BeCM also receives a Heated Rear Window
(HRW) request signal from the HEVAC ECU in the
form of a momentary completion of an earth path
when either the manual HRW switch is depressed or
the programmed demist switch is depressed. When
the BeCM receives the request, it energises an
internal relay and supplies a 12 V supply to the HRW
element via fuse 12.
LH and RH seat heater request signals are also
generated by the HEVAC ECU in the form of a
momentary completion of an earth path when the
applicable switch is depressed. The BeCM outputs a
12 V supply to the requested seat heater element,
provided that the ignition is in position II and the
engine is running.
See HEATING AND
VENTILATION, Description and operation.
Anti-Lock Braking System ECU
The BeCM communicates with the ABS ECU via
hardwired connections. The BeCM receives inputs
from the ABS ECU for ETC/ABS warning lamp
illumination and message centre displays to the
instrument pack.
Inputs are also passed from the ABS pressure switch
in the form of completed earth paths for ABS warning
lamp operation.
The ABS ECU generates a road speed signal which is
passed to the BeCM. The BeCM uses the road speed
signal and also passes it to other ECU’s to control
various vehicle functions.
See BRAKES, Description
and operation.
Electronic Automatic Transmission ECU
The BeCM is connected via hardwired connections to
the EAT ECU. The BeCM receives inputs from the
gearbox position switch and generates outputs to the
selector lever cover illumination for gear position LED
illumination. Outputs are also provided to the
instrument pack message centre for gear positions.
The BeCM outputs an engine speed signal to the EAT
ECU and also transfers diagnostic information from
the ECU to the diagnostic socket.
See AUTOMATIC
GEARBOX, Description and operation.
