Range Rover 2. Electrical Manual - part 161

CRUISE CONTROL

CIRCUIT OPERATION

REV: 08/99

System Disable

The cruise control system can be disabled in one of
four ways:

1. The Cruise Control Switch (X115) is put in the 0

position, removing the BeCM (Z238) power from
the Cruise Control ECU (Z121) and vacuum
pump, and erasing the set speed memory.

2. The RES/DECEL Switch is depressed, signalling

the Cruise Control ECU (Z121) via the Inverter/
Converter (Z249) to disengage the system.

3. The brake pedal is depressed and a vacuum val-

ve in the Switch Vent Valve opens (X112). This
vents vacuum to the actuator valve and releases
the throttle.

4. The Voltage applied to the Cruise Control ECU

(Z121) terminal 1 is interrupted, causing the
Cruise Control ECU (Z121) to turn off the
vacuum pump and de–energize the vacuum
solenoid valve. This voltage path is interrupted
when:

The brake pedal is depressed. With the brake
pedal depressed, the Brake Switch Vent Valve
(X112) moves to position 1 and the circuit is in-
terrupted.

The transfer gear box is not in Hi range.

The vehicle speed does not exceed 28 mph (45
km/h).

The vehicle is not in a forward gear (P, R, or N)
(Automatic Transmission).

The clutch pedal is depressed (Manual
Transmission).

The engine rpm rises above 5000

10%

(Manual Transmission).

The BeCM (Z238), which monitors these signals, will
then remove power from C1279/Pin 18.

Diesel Engine

For vehicles equipped with a manual transmission,
cruise control can only be activated when the Cruise
Control Switch (X115) is depressed and the clutch
pedal is not depressed. The Diesel Engine Control
Module (Z132) will not allow the engine to overspeed
if a cruise control speed is requested that is beyond
the capability of the engines speed range.

For vehicles equipped with an automatic
transmission, cruise control can only be activated
when the Cruise Control Switch (X115) is depressed,
the transfer gear box is in Hi range, and the
transmission is in one of the forward gears.

With the Cruise Control Switch (X115) on, a ground
signal is applied to C1279/Pin 14 of the BeCM
(Z238). The X, Y, and Z switch status (PRND321
position information) from the gearbox position
switch is applied to C1287/Pins 8, 9, and 18 of the
BeCM (Z238). The clutch pedal position input is
applied to C1279/Pin 4 and the engine speed input is
applied to C1288/Pin 9 of the BeCM (Z238). The
BeCM (Z238) then supplies voltage, via its Pin 18 to
the Inverter/Converter (Z249) and to the “Operation”
bulb of the Cruise Control Switch (X115).

The Cruise Control Converter/Inverter Module
(Z249) supplies the Engine Control Module (Z132)
via its pin 4 with a voltage signal to “switch on” the
cruise circuit. For the Diesel Engine, the Engine
Control Module (Z132) controls the cruise circuit as
the Cruise Control ECU (Z121) does for the Petrol
Engine. The Engine Control Module (Z132) is also
responsible for the acceleration/deceleration of the
vehicle.

CRUISE CONTROL

CIRCUIT OPERATION

SET/ACCEL

To set a cruise speed, the Cruise Control Switch
(X115) must be on and vehicle speed must exceed
28 mph (45 km/h). When the SET/ACCEL Switch is
depressed under these conditions, the
Inverter/Converter (Z249) is suppplied with a ground
signal. This signal is transmitted via the OY wire to
the Engine Control Module (ECM) (Z132) causing
the vehicle to accelerate. When the SET/ACCEL
Switch is released, the signal is removed signalling
the Engine Control Module (ECM) (Z132) to set the
speed.

RES

When the RES Switch is depressed, a signal is
applied to the ECM (Z132) and the vehicle will return
to the previously set speed.

Speed Input

The BeCM (Z238) receives the vehicle speed signal
from the Anti–lock Brake System ECU (Z108). The
BeCM (Z238) then provides the vehicle speed signal
to the Engine Control Module (ECM) (Z132). This
signal is a pulsing voltage and its frequency changes
with the vehicle speed.

System Disable

The cruise control system can be disabled in two
ways:

1. The Cruise Control Switch (X115) is put in the 0

position, causing the BeCM (Z238) to remove
power from the Engine Control Module (ECM)
(Z132) and erasing the set speed memory.

2. The Voltage applied via the Inverter/Converter

(Z249) to the Engine Control Module (ECM)
(Z132) terminal 20 is interrupted, causing the
Engine Control Module (ECM) (Z132) to disen-
gage the system. This voltage path is interrupted
when :

The brake pedal is depressed. The Engine
Control Module (ECM) (Z132) has two Stop
Lamp Switch (X168) inputs, each of opposite
polarity. The ECM (Z132) compares the polarity
states to determine when the brake pedal has
been depressed.

The vehicle speed does not exceed 28mph (45
km/h).

The vehicle is not in a forward gear (P, R, or N)
(Automatic Transmission).

The clutch pedal is depressed (Manual
Transmission).

The BeCM (Z238), which monitors these signals, will
then remove power from C1279/Pin 18.

CRUISE CONTROL

CIRCUIT OPERATION

Road Test

CAUTION: DO NOT ENGAGE CRUISE CONTROL
WHEN VEHICLE IS BEING USED IN LOW
TRANSFER GEARS.

WARNING: The use of cruise control is not
recommended on winding, snow covered or slippery
roads, or in heavy traffic conditions where constant
speed cannot be maintained.

1. Start the engine and depress the Cruise Control

Switch (X115) to activate the cruise control
system. Accelerate to approximately 30 mph (50
km/h) and press the SET/ACCEL Switch. Imme-
diately release the switch and remove foot from
the accelerator pedal. The vehicle should main-
tain the speed at which the SET/ACCEL Switch
was pressed.

2. Press the SET/ACCEL Switch and hold at that

position. The vehicle should accelerate smoothly
until the switch is released. The vehicle should
now maintain the new speed at which the SET/
ACCEL Switch was released.

3. Press the RES/DECEL Switch while the vehicle

is in the cruise control mode. The cruise control
should disengage. Slow to approximately 35 mph
(55km/h) and press the RES/DECEL Switch.
Immediately release the switch and remove foot
from the accelerator. The vehicle should
smoothly accelerate to the previously set speed.
Increase speed using the accelerator pedal.
Releasing the pedal should return the vehicle to
the previously set speed.

4. Depressing the brake pedal should immediately

disengage the cruise control system and return
the vehicle to driver’s control at accelerator
pedal. Press the RES/DECEL Switch and the
vehicle should accelerate to the previously set
speed without operation of the accelerator pedal.

5. Press the RES/DECEL Switch and allow the

vehicle to decelerate to below 26 mph (42 km/h).
Press the RES/DECEL Switch and remove foot
from the accelerator pedal. The vehicle should
smoothly adjust to the previously memorized
speed.

6. Press the SET/ACCEL Switch below 28 mph

(45km/h) and the cruise control system should
remain disengaged. Accelerate the vehicle
above 28 mph (45 km/h), press the RES/DECEL
Switch and remove foot from the accelerator
pedal. The vehicle should smoothly adjust to the
previously memorized speed.

7. Pressing the Cruise Control Switch (X115)

should immediately disengage the cruise control

system and erase the previously set speed from
Cruise Control ECU (Z121)/Engine Control
Module (ECM) (Z132) memory.

CRUISE CONTROL (PETROL)

CIRCUIT DIAGRAM

Z238
Body Electrical
Control Module
(BECM)

C0749

C1279

X115
Cruise Control
Switch

See Ground
Distribution

C0749

S208

E0562

Z121
Cruise Control
ECU

C0239

Z249
Cruise Control
Converter/In-
verter Module

C0895P

C0082

Z119
Rotary Coupler

C1254

X269
Steering Wheel
Switches

[6]

Reset/Decel

[7]

Set/Accel

C1254

Z119
Rotary Coupler

See Ground
Distribution

S215

E0562

C0082

C0239

Interior Lamps

[6]

[7]

S202

Petrol

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