1999 LAND ROVER DISCOVERY clutch

ENGINE MANAGEMENT SYSTEM - V8
18-2-68 DESCRIPTION AND OPERATION
Brake pedal switch
The cruise control ECU has two inputs from the brake pedal switch that determine the position of the brake pedal.
One input comes through the BCU and is low when the brake pedal is not pressed. The second input comes directly
from the brake pedal switch. This input is high when the brake pedal is not pressed. On vehicles with a manual
gearbox, the input from the clutch pedal switch to the cruise control ECU is connected in series with the direct signal
from the brake pedal switch.
If the cruise control ECU receives a changed signal from either source, it deactivates cruise control, removing power
to the vacuum pump and activating the vacuum control valve releasing all vacuum in the system.
The brake pedal switch also provides the signal to illuminate the brake lamps and the brake input to the SLABS ECU.
Input/Output
With the brake pedal and the clutch pedal in the rest position, the cruise control ECU receives 12 Volts.
With the brake pedal pressed, the cruise control ECU receives 0 Volts and a low voltage logic signal from the BCU.
NOTE: If the clutch pedal is pressed, 0 Volts are present at the cruise control ECU irrespective of brake pedal position.
ECU operating parameters (connector connected)
Pin No. Condition Volts Ohms
1 Ignition in position II, brake pedal
released, clutch pedal released12
1 Ignition in position II, brake pedal
pressed, clutch pedal releasedMore than 10,000
1 Ignition in position II, brake pedal
released, clutch pedal pressedMore than 10,000

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-69
Clutch pedal switch
The clutch pedal switch is a single pole normally closed switch. It is part of the 12 Volt brake pedal switch circuit to
the cruise control ECU. When the clutch pedal is pressed, the cruise control ECU deactivates the cruise control
system and releases system vacuum. The last set speed is retained in the cruise control ECU.
Input/Output
The cruise control ECU receives a 12 Volt signal through the normally closed contacts of the brake pedal switch and
the normally closed clutch pedal switch.

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-71
Vacuum pump assembly
The vacuum pump assembly contains three components:
lThe vacuum pump.
lThe vacuum control valve.
lThe vacuum dump valve.
The vacuum pump provides the vacuum for the system while the two valves work in conjunction to allow the pump to
increase the vacuum to the pneumatic actuator (increase vehicle speed) or release vacuum from the pneumatic
actuator (decrease vehicle speed). On vehicles from 03 model year, the cruise control vacuum pump and pneumatic
actuator assembly is fitted with a heat shield to protect the components from heat from the exhaust manifold.
The vacuum control valve opens to allow the vacuum pump to increase the vacuum in the pneumatic actuator to
increase vehicle speed. When the vehicle reaches the set speed, the vacuum pump control valve closes to hold
vacuum in the pneumatic actuator and the vacuum pump is turned off by the cruise control ECU.
The vacuum dump valve is normally open. When cruise control is active, the cruise control ECU provides voltage to
close the vacuum dump valve. If power is lost, (e.g. when the brakes or clutch are applied or cruise control is turned
off at the cruise control master switch) the vacuum dump valve will immediately open and cruise control will be
deactivated.
The cruise control ECU provides power for all three components within the vacuum pump assembly. The cruise
control ECU provides earth control circuits for the vacuum pump and the vacuum control valve. The vacuum dump
valve is permanently grounded.
Input/Output
The cruise control ECU provides both power and earth to the components within the vacuum pump assembly. Current
draw at the vacuum pump assembly varies depending on components operating.
Vacuum pump current draw
When cruise is requested, the cruise control ECU provides voltage to the vacuum pump assembly and provides a
pulsed earth signal. The pulse period is dependent on the difference between the vehicle set speed and the actual
road speed. Removing the earth path switches off the pump.
Component State of components
Vacuum dump valve Off On On On
Vacuum control valve Off Off On On
Vacuum pump Off Off Off On
Current draw, amperes 0 0.23 0.37 2.14

ENGINE MANAGEMENT SYSTEM - V8
18-2-74 DESCRIPTION AND OPERATION
Operation - cruise control
Cruise control activation
Cruise control is a passive system. The driver must activate it. Switching on the cruise control master switch located
on the instrument panel activates cruise control. An LED in the switch illuminates, indicating cruise control is
available. The driver must accelerate the vehicle to the desired speed using the accelerator pedal. When the desired
speed is reached, pressing the SET+ switch activates cruise control. Cruise control will only activate if the following
conditions are met:
lVehicle speed is between 28 - 125 mph (45 - 200 km/h).
lThe brake pedal is not pressed.
lThe clutch pedal is not pressed (manual gearbox only).
lThe gearbox is not in park, reverse or neutral (automatic gearbox only).
Function
The cruise control ECU receives the set signal and determines the vehicle speed provided by the SLABS ECU. The
cruise control ECU activates the vacuum pump assembly to move the pneumatic actuator and the linkage to the
throttle disc to maintain set road speed. It does this by controlling the vacuum to the pneumatic actuator.
Cruise control cancellation
Cancelling cruise control enables the driver to regain control of the vehicle speed by using the accelerator pedal.
Cruise control is cancelled if any of the following conditions occur:
lThe brake pedal is pressed.
lThe RES switch button is pressed.
lThe clutch pedal is pressed (manual gearbox only).
lThe cruise control master switch is turned off.
lThe gearbox is placed in park, neutral, or reverse (automatic gearbox only).
Function
The cruise control ECU cancels cruise control operation by opening a vacuum control valve in the vacuum pump
assembly. This releases the throttle linkage from the control of the pneumatic actuator and returns it to the control of
the accelerator pedal.
The set speed will be stored in the cruise control ECU unless:
lThe cruise control master switch is turned off.
lThe ignition switch is turned off.
If cruise control is deactivated using either of the above methods, the set speed will be erased from the memory of
the cruise control ECU.
Cruise control resume
Cruise control can be resumed at the previously set speed, provided the set speed has not been erased from the
cruise control ECU memory as described above. To resume cruise control operation to the previously set speed,
depress the RES switch once when the following conditions are met:
lA set speed is stored in the cruise control ECU.
lVehicle speed is between 28 - 125 mph (45 - 200 km/h).
lThe brake pedal is not pressed.
lThe clutch pedal is not pressed (manual gearbox only).
lThe gearbox is not in park, reverse or neutral (automatic gearbox only).
Function
The cruise control ECU activates the vacuum pump assembly to move the pneumatic actuator. This moves the
throttle to the set speed by adjusting the position of the throttle disc.

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-75
Accelerating while cruise control is active
There are three ways of increasing vehicle speed when cruise control is active:
lTemporarily increase vehicle speed (e.g. when overtaking another vehicle).
lIncrease vehicle set speed in 1 mph (1.5 km/h) increments.
lIncrease vehicle set speed.
To temporarily increase vehicle speed press the accelerator pedal until the desired speed is reached. When the
accelerator pedal is released, the vehicle coasts back to the set speed. When it reaches the set speed, cruise control
operation continues.
To increase the vehicle set speed in 1 mph (1.5 km/h) increments, tap the SET+ switch. Each tap on the switch
increases vehicle speed.
To increase the vehicle set speed, press and hold the SET+ switch until the desired set speed is reached.
The vehicle set speed will increase if the following conditions are met:
lThe vehicle is under cruise control operation.
lVehicle speed is between 28 - 125 mph (45 - 200 km/h).
lThe brake pedal is not pressed.
lThe clutch pedal is not pressed (manual gearbox only).
lThe gearbox is not in park, reverse or neutral (automatic gearbox only).
Function
The vehicle responds as follows:
lIf the driver accelerates using the accelerator pedal, vehicle speed increases overriding pneumatic actuator
position. When the driver releases the accelerator pedal, the vehicle returns to the set speed.
lIf the SET+ switch is tapped, the driver increases the stored speed and vehicle speed by 1 mph (1.5 km/h) per
tap on the switch.
lIf the driver presses and holds the SET+ switch, the vehicle speed increases until the SET+ switch is released.
This becomes the new set speed for the cruise control ECU.
Switching off cruise control
Switching off cruise control allows the driver to regain control of vehicle speed. It erases the set road speed from the
cruise control ECU memory.
To switch off cruise control, press the cruise control master switch to the off position.
Function
When the cruise control master switch is turned off, the cruise control ECU switches off power to the vacuum pump
assembly. The vacuum dump valve opens releasing the vacuum in the pneumatic actuator, returning the throttle disc
to driver control via the accelerator pedal.

ENGINE MANAGEMENT SYSTEM - V8
REPAIRS 18-2-97
Switch - cruise control (set/resume)
$% 19.75.33
Remove
1.Remove the key from the starter switch.
Disconnect both battery leads, negative lead
first. Wait ten minutes before starting work.
2.Remove driver's airbag module.

+ RESTRAINT SYSTEMS, REPAIRS,
Airbag module - drivers.
3.Release remote control switches multiplug and
leads from steering wheel base.
4.Disconnect remote control switches multiplug
from harness.
5.Remove 2 screws securing remote control
switches to steering wheel base.
6.Release and remove remote control switches
from steering wheel.
Refit
1.Fit remote control switches to steering wheel
and secure with screws.
2.Connect remote control switches multiplug to
harness.
3.Secure leads and multiplug to base of steering
wheel.
4.Fit driver's airbag module.

+ RESTRAINT SYSTEMS, REPAIRS,
Airbag module - drivers.
Switch - clutch pedal - cruise control
$% 19.75.34
Remove
1.Remove 3 fasteners and move driver's side
lower closing panel aside.
2.Disconnect multiplug from clutch pedal switch.
3.Remove switch from pedal bracket.
Refit
1.Engage switch fully into pedal bracket location
and connect multiplug.
2.Position lower closing panel and secure with
fasteners.

CLUTCH - V8
DESCRIPTION AND OPERATION 33-2-1
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CLUTCH - V8 DESCRIPTION AND OPERAT ION

CLUTCH - V8
33-2-2 DESCRIPTION AND OPERATION
Clutch components