2002 LAND ROVER DISCOVERY Workshop Manual

FRONT SUSPENSION
60-22 DESCRIPTION AND OPERATION
Failure modes
Failures where the vehicle can still be driven safely are indicated by the ACE warning lamp illuminating continuously
with an amber colour. The amber warning lamp will remain illuminated until the ignition is turned off. For all faults the
warning lamp will only illuminate again if the fault is still present. Failures which require the driver to stop the vehicle
immediately are indicated by the ACE warning lamp flashing with a red colour and an audible warning. All faults are
recorded by the ACE ECU and can be retrieved with diagnostic equipment.
The following tables show the type of system failures and their effects on the system operation. Torsion bar 'floppy'
means that fluid is allowed to circulate freely through the system. With no pressure in the actuators the torsion bar will
have no effect on vehicle roll. 'Locked bars' means that all pump flow is directed through the valve block and returns
to the reservoir. Both DCV's close and fluid is trapped in the actuators but can flow from one actuator to the other via
the valve block. In this condition the torsion bar will perform similar to a conventional anti-roll bar, resisting roll but still
allowing the axles to articulate.
Acceleration sensors
Pressure transducer
14 Reverse switch Input
15 Accelerometer - lower (signal) Input
16 Pressure transducer (signal) Input
17 Accelerometer - upper (signal) Input
18 Accelerometer - upper (supply) Output
19 Engine speed Input
20 Main earth 1 -
21 Pressure transducer (earth) Input
22 DCV 2 (earth) Input
23 DCV 1 (earth) Input
24 DCV 1 & 2 (supply) Output
25 Pressure control valve (earth) Input
26 Not used -
27 Pressure control valve (supply) Output
28 Main supply (+ V Batt) Input
29 to 31 Not used -
32 Main earth 2 -
33 Accelerometer - lower (signal) Input
34 Accelerometer - upper (signal) Input
35 Not used -
36 Warning lamp Output
Failure Effect
Valve stuck closed No ACE control
Short circuit - Ground No ACE control
Short circuit - VBatt No ACE control
Loose sensor Erractic ACE activity when driving in straight line
Failure Effect
Short circuit - VBatt Large sensor dead band - possible random movementsPin No. Description Input/Output

FRONT SUSPENSION
DESCRIPTION AND OPERATION 60-23
Road speed signal
Engine speed signal
Reverse gear signal
Ignition ON signal
Pressure control valve failure
Failure Effect
Open circuit No ACE control - 'Locked bars' condition
Short circuit - Ground No ACE control - 'Locked bars' condition
Short circuit - VBatt No ACE control - 'Locked bars' condition
Failure Effect
Open circuit No ACE control - 'Locked bars' condition
Short circuit - Ground No ACE control - 'Locked bars' condition
Short circuit - VBatt No ACE control - 'Locked bars' condition
Failure Effect
Open circuit No reverse signal to ECU. ACE active in reverse, may give
abnormal handling when reversing
Short circuit - Ground No reverse signal to ECU. ACE active in reverse, may give
abnormal handling when reversing
Short circuit - VBatt Permanent reverse signal to ECU. Permanent 'Locked
bars' condition
Failure Effect
Open circuit ECU does not receive ignition ON signal. No ARC control,
'Locked bars' condition
Short circuit - Ground ECU does not receive ignition ON signal. No ARC control,
'Locked bars' condition
Short circuit - VBatt Permanent ignition ON signal to ECU. Possibility of flat
battery
Failure Effect
Open circuit No ACE control
Short circuit - Ground No ACE control
Short circuit - VBatt No ACE control
Valve stuck open No ACE control
Valve stuck closed Maximum system pressure - no proportional control.
Pressure relief valve operating at 185 bar (2683 lbf.in
2)

FRONT SUSPENSION
60-24 DESCRIPTION AND OPERATION
Directional control valves
Failure Effect
DCV 1 DCV 2
Valve open or stuck open Valve open or stuck open No ACE control - Anti-roll bars floppy
Valve closed or stuck closed Valve closed stuck closed No ACE control - 'Locked bars' condition (default)
Valve open or stuck open Valve closed or stuck closed Vehicle leans to left when pressure is applied to actuators
Valve closed or stuck closed Valve open or stuck open Vehicle leans to right when pressure is applied to actuators

FRONT SUSPENSION
DESCRIPTION AND OPERATION 60-25
Operation
Hydraulic circuit diagram
1Pressure transducer
2Directional control valve 2
3Front torsion bar assembly
4Actuator
5Actuator
6Rear torsion bar assembly
7Directional control valve 18Valve block
9Pressure control valve
10Reservoir
11Filter
12High pressure filter
13Hydraulic pump
14Attenuator hose
Vehicle not moving
When the engine is running and the vehicle is not moving, both DCV's are closed, locking fluid in each side of the
actuator pistons. The hydraulic pump draws fluid from the reservoir and passes it at very low pressure to the valve
block. Because both DCV's are closed, after the fluid passes through the high pressure filter, it is directed through the
pressure control valve to the reservoir. The pressure control valve is open fully to allow the full flow to pass to the
reservoir. The DCV's will remain closed until the ECU detects a need to operate.

FRONT SUSPENSION
60-26 DESCRIPTION AND OPERATION
Vehicle moving and turning left
When the vehicle is turning left, the accelerometers detect the cornering forces applied and transmit signals to the
ECU. The ECU determines that an opposing force must be applied to the torsion bars to counter the cornering forces.
The ECU supplies a current to the solenoid of the DCV2. Simultaneously, a current is sent from the ECU to the
pressure control valve which operates to restrict the flow of fluid returning to the reservoir.
The restriction causes the hydraulic pressure in the system to rise and the pressure is sensed by the pressure
transducer which sends a signal to the ECU. The ECU determines from the inputs it receives what pressure is required
and adjusts the pressure control valve accordingly.
The pressure in the system is applied to the annulus of each actuator, applying an opposing force to the torsion bar
and minimising the cornering effect on the vehicle and maintaining the vehicle attitude. The fluid displaced from the
full area of the actuator is returned to the reservoir via the valve block.
As the cornering force is removed when the vehicle straightens up, the ECU opens the pressure control valve to
reduce the pressure in the system. The fluid bleeds from the actuator back into the system as the cornering force is
reduced, removing the force from the torsion bar. When the vehicle is moving in a straight line DCV 2 closes.
Vehicle moving and turning right
When the vehicle is turning right, the accelerometers detect the cornering forces applied and transmit signals to the
ECU. The ECU determines that an opposing force must be applied to the torsion bars to counter the cornering forces.
The ECU supplies a current to the solenoid of the DCV1. Simultaneously, a current is sent from the ECU to the
pressure control valve which operates to restrict the flow of fluid through the by-pass gallery.
The restriction causes the hydraulic pressure in the system to rise and the pressure is sensed by the pressure
transducer which sends a signal corresponding to the pressure to the ECU. The ECU determines from the inputs it
receives what pressure is required and adjusts the pressure control valve accordingly.
The pressure in the system is applied to the full area of each actuator, applying an opposing force to the torsion bar
and minimising the cornering effect on the vehicle and maintaining the vehicle attitude. The fluid displaced from the
annulus of the actuator is returned to the reservoir via the valve block.
As the cornering force is removed when the vehicle straightens up, the ECU opens the pressure control valve to
reduce the pressure in the system. The fluid bleeds from the actuator back into the system as the cornering force is
reduced, removing the force from the torsion bar. When the vehicle is moving in a straight line the DCV 1 closes.
Vehicle moving in a straight line
The ECU is constantly monitoring the signals received from the accelerometers and operates the DCV's and pressure
control valve to maintain the vehicle attitude when the vehicle is moving.
Off-road driving
Off-road detection is achieved by the ECU by monitoring the signals from the upper and lower accelerometers for
varying degrees of body movement. Off-road driving generates differing signals to the accelerometers which in turn
produce differing outputs due to their vertical separation and the location of the roll centre of the vehicle. The two
signals are passed through a filter to remove any offset caused by the vehicle leaning or the terrain. The ECU then
uses this signal to calculate the percentage of road roughness.
Below 25 mph (40 km/h) the percentage of road roughness calculated is used by the ECU to limit the operation of the
ACE system. The system is completely inoperative at speeds below 2 mph (3 km/h). At speeds above 25 mph (40
km/h) the system disables the percentage road roughness signal and full ACE system assistance is restored.
Side slope detection
The ECU uses side slope detection when the upper and lower accelerometers detect an average acceleration of more
than
± 0.2 g and a road speed of less than 25 mph (40 km/h).
When side slope is detected both DCV's close to provide a 'locked bars' condition. This condition increases stability
and gives a consistent vehicle response. As the road speed increases up to 25 mph (40 km/h), the level of average
lateral acceleration must also increase and be maintained for the system to recognise that the vehicle is on a side
slope. If the side slope angle is steep and the road speed is low, the ECU will detect the side slope in a short time.

FRONT SUSPENSION
ADJUSTMENTS 60-27
ADJUST ME NTS
ACE hydraulic system bleeding
$% 60.60.13
Introduction
CAUTION: The ACE hydraulic system is
extremely sensitive to the ingress of dirt or
debris. The smallest amount could render the
system unserviceable. It is imperative that the
following precautions are taken.
lACE components are thoroughly cleaned
externally before work commences;
lall opened pipe and module ports are
capped immediately;
lall fluid is stored in and administered
through clean containers.
Check
1.Check the ACE system fluid level.

+ FRONT SUSPENSION,
ADJUSTMENTS, Fluid level check - ACE
system.
Bleed
1.With vehicle on ramp, connect TestBook and
follow bleed procedure as described.
Fluid level check - ACE system
$% 60.60.14
Introduction
CAUTION: The ACE hydraulic system is
extremely sensitive to the ingress of dirt or
debris. The smallest amount could render the
system unserviceable. It is imperative that the
following precautions are taken.
lACE components are thoroughly cleaned
externally before work commences;
lall opened pipe and module ports are
capped immediately;
lall fluid is stored in and administered
through clean containers.
Check
1.Clean reservoir around fluid level marks.
2.Visually check fluid level through side of
reservoir. Fluid level must be between upper
and lower fluid level marks.
Top-up
1.Clean reservoir around filler cap.
2.Remove filler cap from reservoir and fill to
upper fluid level mark with recommended fluid.

+ CAPACITIES, FLUIDS AND
LUBRICANTS, Fluids.
3.Fit filler cap to reservoir
4.Start and run engine for 2 minutes to circulate
fluid.
5.If necessary, top-up reservoir to upper fluid
level mark.

FRONT SUSPENSION
60-28 ADJUSTMENTS

FRONT SUSPENSION
REPAIRS 60-29
REPAIRS
Bushes - Panhard rod
$% 60.10.07
Remove
1.Raise front of vehicle.
WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.
2.Remove 2 nuts and bolts securing Panhard rod
to axle and chassis.
3.Remove Panhard rod from vehicle.
4.Use tool LRT-60-013 fitted with LRT-60-013/1
and LRT-60-013/3 to press out bushes from
Panhard rod. Refit
1.Clean bush locations in Panhard rod.
2.Use tool LRT-60-013 fitted with LRT-60-013/1
and LRT-60–013/2 to press new bushes into
Panhard rod. Ensure pressure is applied to
the outer edge of the bush, not the rubber
inner.
3.Position Panhard rod to axle and chassis.
4.Fit bolts securing Panhard rod but do not
tighten at this stage.
5.Remove stand(s) and lower vehicle.
6.Tighten bolts securing Panhard rod to 230 Nm
(170 lbf.ft).
CAUTION: Nuts and bolts must be tightened
with weight of vehicle on suspension.