Discovery 2. Manual - part 496

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-63

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

18-2-64 DESCRIPTION AND OPERATION

Vacuum pump assembly

The vacuum pump assembly contains three components:

The vacuum pump.

The vacuum control valve.

The 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

Component

State of components

Vacuum dump valve

Off

Vacuum control valve

Off

Vacuum pump

Off

Current draw, amperes

0.23

0.37

2.14

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-65

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.

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.

5 Output 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.

6 Output 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.

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

18-2-66 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:

Vehicle speed is between 28 - 125 mph (45 - 200 km/h).

The brake pedal is not pressed.

The clutch pedal is not pressed (manual gearbox only).

The 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:

The brake pedal is pressed.

The RES switch button is pressed.

The clutch pedal is pressed (manual gearbox only).

The cruise control master switch is turned off.

The 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:

The cruise control master switch is turned off.

The 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:

A set speed is stored in the cruise control ECU.

Vehicle speed is between 28 - 125 mph (45 - 200 km/h).

The brake pedal is not pressed.

The clutch pedal is not pressed (manual gearbox only).

The gearbox is not in park, reverse or neutral (automatic gearbox only).

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