1999 LAND ROVER DISCOVERY engine

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-67
SET+/RES switches
The cruise control system uses two steering wheel switches labelled SET+ and RES.
The SET+ switch performs the set speed, tap up and accelerator functions. The RES switch performs the resume and
suspend functions.
With the cruise control master switch on and the vehicle in the cruise control operating speed range, one press of the
SET+ switch stores a speed value in the cruise control ECU. If the switch is pressed and held while the vehicle is
under cruise control operation, speed increases until the switch is released. At this point the cruise control ECU stores
the new speed value. If the switch is tapped (held down for less than 0.5 second) the cruise control ECU increases
vehicle speed by 1 mph (1.5 km/h).
If the RES switch is pressed while the systems is inactive (no stored values) the system will not respond. If there is
a stored value in the cruise control ECU memory and the switch is pressed, the cruise control system operates and
holds the vehicle at the stored road speed. If the cruise control system is active and the RES switch is depressed,
the cruise control ECU deactivates cruise operation but maintains the current set speed value.
Input/Output
The input from the SET+ switch to the cruise control ECU is either 12 Volts or an open circuit.
The input from the RES switch to the cruise control ECU is either 12 Volts or an open circuit.
The following diagnostic information is available through TestBook:
lThe state of operator switch SET+.
lThe state of operator switch RES.
ECU operating parameters (connector connected)
Pin No. Condition Volts Ohms
4 Ignition in position II, SET+ switch
releasedMore than 10,000
4 Ignition in position II, SET+ switch
pressed12
2 Ignition in position II, RES switch
releasedMore than 10,000
2 Ignition in position II, RES switch
pressed12

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
18-2-70 DESCRIPTION AND OPERATION
Body control unit
On manual gearbox vehicles, the BCU provides cruise control lockout or suspend function as described under brake
pedal switch.
On vehicles with automatic gearbox, the BCU monitors the status of the brake pedal switch as well as the status of
the automatic gearbox gear selector lever. The BCU monitors the gear selector lever to determine which gearbox
position the driver has selected. If the BCU detects that the driver has selected park, reverse or neutral, it sends a
signal to the cruise control ECU which inhibits cruise operation or deactivates cruise control if it is activated.
Input/Output
If the BCU receives a brake pedal switch signal or an automatic gearbox gear selector lever position signal, the BCU
sends a HIGH signal to the cruise control ECU. The cruise control ECU cancels or inhibits cruise control functions.

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
18-2-72 DESCRIPTION AND OPERATION
Several fault codes can be generated:
Fault codes
1"Output power LOW when HIGH is expected" is flagged when Pin C0239-11 is shorted to earth.
This could be due to an external fault or an internal ECU fault and will be set if pin C0239-11 is LOW for longer
than 240 milliseconds, while in cruise mode.
2"Output power HIGH when LOW is expected" is flagged when Pin C0239-11 is shorted to battery voltage.
This could be due to an external fault or internal ECU fault and will be set if pin C0239-11 is HIGH for longer than
250 milliseconds while not in cruise mode.
3"Output pump LOW, when High is expected" is flagged when Pin C0239-7 is shorted to earth.
This could be due to an external fault or an internal ECU fault. This fault will be set if pin C0239-11 is HIGH for
longer than 7.5 milliseconds while pin C0239-7 is LOW for longer than 2.5 milliseconds while decelerating under
control of cruise.
4"Output pump HIGH, when LOW is expected" is flagged when Pin C0239-7 is shorted to battery voltage.
This could be due to an external fault or an internal ECU fault. This fault will be set if pin C0239-7 is LOW for
longer than 7.5 milliseconds of the last 8 pulses when the pump is switched on while accelerating under the
control of cruise.
5Output valve LOW, when HIGH is expected is flagged when Pin C0239-7 is shorted to battery voltage.
This could be due to an external fault or an internal ECU fault and will be set if pin C0239-17 is LOW for longer
than 2.5 milliseconds while pin C0239-7 is HIGH for longer than 2.5 milliseconds and pin C0239-11 is also HIGH
for longer than 7.5 milliseconds, while decelerating under control of the cruise control ECU.
6Output valve HIGH, when LOW is expected is flagged when Pin C0239-17 is shorted to battery voltage.
This could be an external fault or an internal ECU fault. The fault will be set if pin C0239-17 remains HIGH for
longer than 35 milliseconds after the vacuum control valve is switched on, while accelerating under control of
the cruise control ECU.
TestBook can be used to determine the fault codes present as well as the general status of the system.

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-73
Pneumatic actuator
The cruise control ECU controls the position of the throttle disc by regulating the amount of vacuum applied by the
vacuum pump to the pneumatic actuator. The pneumatic actuator is an air tight bellow coupled to the pneumatic pump
via a vacuum pipe. The pump evacuates the air inside the bellow and pipe, which collapses the bellow. This pulls on
a cable, which moves the throttle disc to the desired position. 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.

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.