Part 2

Vehicle Dynamic Suspension

Cornering
If the air suspension control module registers a cornering force greater than 0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the cornering force falls to less than 0.15g. The air suspension control module receives a message from the lateral acceleration sensor (which is an integral part of the ABS yaw rate sensor) on the high speed CAN bus for the cornering force.
Rapid Acceleration
If the air suspension control module registers a rapid acceleration greater than 0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the rapid acceleration falls to less than 0.15g. Acceleration is calculated by the air suspension control module from a vehicle speed signal received via the high speed CAN bus.
Rapid Deceleration
If the air suspension control module registers a rapid deceleration smaller than -0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the rapid deceleration rises above -0.15g. Deceleration is calculated by the air suspension control module from a vehicle speed signal received via the high speed CAN bus.
Vehicle Jack
The air suspension control module will inhibit all height changes and corrections if it detects a corner lowering too slowly for more than 1.2 seconds. This is interpreted as the corner identified as moving too slowly being supported on a jack. In this situation, the corner height will not change when air is released from the air spring because the jack acts as a mechanical prop. The system will remain inhibited until any of the following conditions exist:
- The air suspension switch is moved to the up or down position
- Vehicle speed rises to more than 2 mph (3 km/h) for more than 45 seconds.
Door Open
The air suspension control module will stop all height change requests while any of the doors are open. Vehicle leveling continues with a door open by keeping the vehicle at the height when the door was opened if the vehicle load changes.

Diagnostics
The air suspension control module can store fault codes which can be retrieved using the Land Rover approved diagnostic equipment. The diagnostic information is obtained via the diagnostic socket which is located in the lower instrument panel closing panel, on the driver's side, below the steering column.
The diagnostic socket allows the exchange of information between the various control modules on the bus systems, and the Land Rover approved diagnostic equipment. This allows the fast retrieval of diagnostic information and programming of certain functions using the Land Rover approved diagnostic equipment.
Fault Detection
The air suspension control module performs fault detection and plausibility checks. Fault detection is limited to faults that the control module can directly measure as follows:
- Sensor electrical hardware faults
- Valve electrical hardware faults
- Sensor and actuator supply faults
- Bus failures
- Control module hardware errors.
Plausibility checks are checks on signal behavior, as follows:
- Average height does not change correctly
- Height changes too slowly
- Gallery pressure
- Does not increase fast enough when reservoir filling requested
- Increases when system is inactive
- Too low when lifting is requested
- Increases too rapidly when filling reservoir
- Does not decrease when gallery is vented
- Pressure varies too much when inactive.
- Compressor temperature
- Sensor voltage too large - head and brush sensors (short circuit to battery)
- Takes too long to be readable after suitable compressor run time - head and brush sensors
- Does not increase when compressor active - head sensor only
- Sensor activity
- Signal floating
- Constant articulation when moving
When a fault is detected, the air suspension control module will attempt to maintain a comfortable ride quality and where possible will retain as much functionality as possible.
The system functionality depends on the severity of the fault.
Faults
Faults are categorized into order of severity and effect on the system as follows (with 1. being a minor fault and 5. being a major fault):
- Height sensor faults (hardware faults) and reservoir valve block failure
- Retain full functionality with no 'refinements', e.g. cross-link valves inoperative, no compensation for uneven surfaces.
- Pressure sensor faults, compressor faults, corner valves stuck shut
- Road speed signal not available
- Vehicle returns to on-road mode height when next requested
- Levels at 'current' height.
- Reservoir valve stuck open, exhaust valve stuck shut if below on-road mode height, corner valves stuck open if above on-road mode height
- Vehicle returns to on-road mode height when next requested
- Does not level at 'current' height.
- Failure of multiple height sensors, cross-articulation when driving, calibration corrupted
- Vehicle lowers to bump stops.
- ABS module failure, CAN bus failure
- If the air suspension control module loses communications with the ABS module or the ABS module reports a fault, the air suspension control module immediately returns to the 'default' height, which is below the on-road ride height. Once at the default height, the control module will continue to level the vehicle at this height. It is unlikely that the fault will be in the air suspension control module. When the fault is repaired, the air suspension control module will resume full functionality but the error will remain in the control module memory.
For major faults the control module will not level the vehicle at the 'current' ride height. The control module freezes height changes until it receives a manual or automatic request for height change. The control module will return to standard height if possible and freezes once standard height is achieved.
If the suspension is above the on-road height and the air suspension control module cannot lower the suspension, all height changes will be frozen. The control module will issue a message on the high speed CAN bus which is received by the instrument cluster which displays a maximum advisable speed in the message center. an immediate 'freeze' of the vehicle height is caused by the following:
- Failure of more than one height sensor - vehicle on bump stops
- Implausible articulation symptoms detected - vehicle on bump stops
- Valve or solenoid failure - corner valve stuck open below on-road mode height or exhaust valve stuck shut above on-road mode height
- Stuck corner or whole vehicle (diagnosed using plausibility of the sensor inputs).
If height change is not possible, e.g. exhaust valve failed closed at off-road height or compressor failed at access height, the control module will not level or change height.
If the air suspension control module has a hardware fault, the control module will disable all air suspension functions. Detectable hardware errors include memory error, control module failure, calibrations errors.
Fault Messages
The air suspension has two methods which it can use to inform the driver of a fault in the air suspension system; the air suspension switch LED's and the instrument cluster message center.
When minor faults occur and the air suspension control module is able to level the vehicle to the 'current' ride height, the air suspension switch LED's will display the current ride height.
If the air suspension control module suffers a major failure and there is no air suspension control, all the control switch LED's will remain off.
If a fault occurs and the air suspension control module can determine the ride height and the vehicle is not above on-road mode height, the driver will be notified via an 'air suspension fault max speed 30 mph (50 km/h)' message, displayed in the message center.
If the control module cannot determine the height of the vehicle, or the vehicle is above on-road mode height, cannot be lowered and the vehicle speed is too high, an air suspension fault message is displayed.
If the vehicle is restricted to on-road mode height an air suspension fault normal height only message is displayed.

AIR SUSPENSION SWITCH









The air suspension control switch is located in the center console, behind the manual or automatic transmission selector lever. The switch is a three position, non-latching switch which allows selection of the following driver selectable modes:
- Off-road mode
- On-road mode
- Access mode
- Crawl (locked at access) mode.
The air suspension switch can be moved forwards or backwards from its central position. The switch is non-latching and returns to the central position when released. The switch completes an earth path to the air suspension control module when operated. This earth path is completed on separate wires for the raise and lower switch positions, allowing the control module to determine which selection the driver has made.
The switch has six symbols which illuminate to show the current selected height and the direction of movement. The raise and lower symbols will flash and a warning tone will be emitted from the instrument cluster sounder when a requested height change is not allowed, i.e. vehicle speed too fast.
A flashing symbol indicates that the air suspension system is in a waiting state or that the system will override the driver's selection because the speed threshold is too high.
The driver can also ignore the system's warnings signals and allow the height to change automatically. For example, increasing the vehicle speed to more than 25 mph (40 km/h) will cause the control module to automatically change the ride height from off-road mode to on-road mode.

FRONT AND REAR AXLE VALVE BLOCKS









The front and rear axle valve blocks are similar in their design and construction and control the air supply and distribution to the front or rear pairs of air spring damper modules respectively. The difference between the two valves is the connections from the valve block to the left and right hand air spring damper modules and the valve size. It is important that the correct valve block is fitted to the correct axle. Fitting the incorrect valve block will not stop the air suspension system from functioning but will result in slow raise and lower times and uneven raising and lowering between the front and rear axles.
The front valve block is attached to the right hand end of the front bumper armature assembly. The valve block has three attachment lugs which are fitted with isolation rubber mounts. The rubber mounts locate in slots in the armature. The valve lugs locate in the holes above the slots and are pushed downwards into positive location in the slots.
The rear valve block is located on the forward face of the left hand rear suspension turret. The valve block has three attachment lugs which are fitted with isolation rubber mounts which locate in a bracket with three slotted holes. The bracket is attached to the left hand side of the chassis. The isolation rubber mounts locate in the 'V' shaped slots and are pushed downwards into positive location in the slots.
The front and rear valve blocks each have three air pipe connections which use 'Voss' type air fittings. One connection is an air pressure inlet/outlet from the reservoir valve block. The remaining two connections provide the pressure connections to the left and right hand air springs.
Each valve block contains three solenoid operated valves; two corner valves and one cross-link valve. Each of the valve solenoids is individually controlled by the air suspension control module. The solenoids have a resistance value of 2 Ohms at a temperature of 20°C (68°F).

Corner Valves
The corner valves control the flow of air into and out of the individual air springs. When the solenoid is de-energized, the corner valves are held in a closed position by internal springs. When the solenoid is energized, the valve armature moves and allows air to flow into or out of the air spring.

Cross Link Valves
The cross-link valve provides a connection between the two air springs on the same axle. When de-energized, the cross-link valve prevents air passing from one air spring to another. When the solenoid is energized, the valve spool moves and allows air to pass from one air spring to the other. This increases wheel articulation and improves ride comfort at low vehicle speeds.

RESERVOIR VALVE BLOCK









The reservoir valve block controls the storage and distribution of air from the reservoir. The reservoir valve block also contains the system pressure sensor.
The reservoir valve block is attached to a bracket on the outside of the left hand chassis rail, between the reservoir and the air supply unit. The valve block is located within the air supply unit acoustic box to protect it from dirt ingress and damage from stones. The valve block has three attachment lugs which are fitted with isolation rubber mounts which locate in the chassis bracket which has three slotted holes. The isolation rubber mounts locate in the 'V' shaped slots and are pushed downwards into positive location in the slots.
The valve block has four air pipe connections which use 'Voss' type air fittings. The connections provide for air supply from the air supply unit, air supply to and from the reservoir and air supply to and from the front and rear valve blocks. The connections from the air supply unit and the front and rear control valves are all connected via a common gallery within the valve and therefore are all subject to the same air pressures.
The valve block contains a solenoid operated valve which is controlled by the air suspension control module. The solenoid valve controls the pressure supply to and from the reservoir. The solenoid has a resistance value of 2 Ohms at a temperature of 20°C (68°F). When energized, the valve spool moves allowing air to pass to or from the reservoir.
The valve block also contains a pressure sensor which can be used to measure the system air pressure in the air springs and the reservoir. The pressure sensor is connected via a harness connector to the air suspension control module. The control module provides a 5V reference voltage to the pressure sensor and monitors the return signal voltage from the sensor.
Using this sensor, the control module controls the air supply unit operation and therefore limits the nominal system operating pressure to 244 lbf/in2 (16.8 bar gage).

AIR SUPPLY UNIT









The air supply unit is located on the outside of the left hand chassis rail, forward of the upper control arm. The unit is attached to the chassis rail with three bolts and is protected by an acoustic box.

Acoustic Box









The acoustic box, which comprises of two parts; upper and lower, surrounds the air supply unit. The acoustic box is a plastic molding which is lined with an insulating foam which controls the operating noise of the air supply unit. The reservoir valve block is also located in the acoustic box, forward of the air supply unit.
The air supply unit comprises the following major components:
- A piston compressor
- A 12V electric motor
- A solenoid operated pilot valve
- An exhaust valve
- An air dryer unit
The air supply unit can be serviced in the event of component failure, but is limited to the following components; air dryer, pilot exhaust pipe and the rubber mounts.
The air supply unit is attached to a bracket which is bolted to the chassis. The unit is mounted to the bracket with flexible isolation mounting rubbers which assist with preventing operating noise being transmitted to the chassis.
Removal of the air supply unit does not require the whole air suspension system to be depressurized. The front and rear valve blocks and the reservoir valve block are normally closed when de-energized, preventing air pressure in the air springs and the reservoir escaping when the unit is disconnected.
There are a number of conditions that will inhibit operation of the air supply unit. It is vitally important that these system inhibits are not confused with a system malfunction. A full list of air supply unit inhibits are given in the air suspension control module section in this chapter.

Air Supply Unit - Sectional View









Pilot Exhaust Valve
A solenoid operated pilot exhaust valve is connected to the air delivery gallery, downstream of the air dryer. The pilot valve, when opened, operates the main compressor exhaust valve. This allows the air springs to be deflated when required.
When the solenoid is energized, pilot air moves the exhaust valve plunger, allowing pressurized air from the air springs and/or reservoir to pass via the reservoir control valve to the air supply unit.
The solenoid has a resistance value of 4 Ohms at a temperature of 20°C (68°F).

Exhaust Valve
The exhaust valve has three functions. It operates in conjunction with the pilot exhaust valve to allow air to be exhausted from the air springs and/or the reservoir as described previously.
The valve also protects the system from over-pressure. The valve is connected into the main pressure gallery which is always subject to the system pressure available in either the air springs or the reservoir. The valve is controlled by a spring which restricts the maximum operating pressure to between 333.5 to 370 lbf/in2 (23.0 to 25.5 bar).
The minimum pressure in the system is also controlled by the exhaust valve to ensure that, even when deflated, the air springs contain a positive pressure of approximately 14.5 lbf/in2 (1 bar gage) with respect to atmosphere. This protects the air spring by ensuring it can still 'roll' over the piston without creasing.

Electric Motor
The electric motor is a 12V dc motor with a nominal operating voltage of 13.5V. The motor drives a crank which has an eccentric pin to which the compressor connecting rod is attached.
The motor is fitted with a temperature sensor on the brush PCB assembly. The sensor is connected to the air suspension control module which monitors the temperature and can suspend motor operation if an overheat condition occurs.

Compressor
The compressor comprises a motor driven connecting rod and piston which operate in a cylinder with a cylinder head. The motor rotates the crank moving the piston up and down in the cylinder bore. The air in the cylinder is compressed with the up stroke and is passed via delivery valve, through the air dryer into the system.

Air Dryer
The air dryer is an integral part of the air supply unit. The air dryer contains a desiccant which absorbs moisture. Pressurized air is passed through the air dryer which removes any moisture in the compressed air before it is passed to the reservoir and/or the system
When the air is exhausted from the system, the returning air is passed through the air dryer, regenerating the air dryer by removing moisture from the desiccant and expelling it to atmosphere via the exhaust.
The air dryer is an essential component in the system ensuring that only dry air is present in the system. If moist air is present in the system, freezing can occur, resulting in poor system operation or component malfunction/failure.

AIR RESERVOIR









The reservoir is an air storage vessel which provides fast air suspension lift times by the immediate availability of pressurized air into the system.
The reservoir is a steel fabrication and is located on the outside of the left hand chassis rail, in front of the air supply unit. The reservoir has a bracket at each end which attach to the body mounting brackets on the chassis.
The rearward end of the reservoir has a 'Voss' air fitting which provides for the connection of the air hose between the reservoir and the reservoir valve block.
The reservoir has a capacity of 550 in3 (9 liters). The nominal working pressure of the reservoir is 243.6 lbf/in2 (16.8 bar gage), with a maximum pressure of 333.5 lbf/in2 (23 bar gage).

HEIGHT SENSORS

Front Height Sensor









Rear Height Sensor









A height sensor is fitted in each corner of the vehicle to monitor the ride height of the vehicle. The sensor bodies are attached with screws to brackets on the chassis rails.
Each sensor comprises a sensor body which contains a single track rotary potentiometer, a lever arm and a drop link.
The sensor lever arm has a drop link which provides the connection between the sensor and the suspension control arm. The drop link is a serviceable component and is a push fit to the lever arm and the suspension control arm.
The sensors are connected via their harness connector to the air suspension control module which receives the signal output from each sensor and, using preprogrammed information, converts the signal to a height for each sensor position.
The front and rear sensors are handed and are colored coded for identification as follows:
- Right hand front and rear - black colored lever
- Left hand front and rear - white colored lever.

Calibration
A calibration routine is performed using the Land Rover approved diagnostic equipment to read the position of each corner of the vehicle, and record the settings in the ECU memory. Once set, the calibration is not required to be performed unless the air suspension control module is removed or replaced, a height sensor is removed or replaced or a suspension arm to which the sensor is connected is removed or replaced. If the removed height sensor is subsequently refitted, the calibration procedure will have to be performed to ensure the integrity of the system.
If a replacement drop link is fitted, recalibration is not required providing the sensor body is not removed from its mounting bracket.

AIR SILENCER AND INLET AIR FILTER









The air silencer is required to limit any noise produced from the air supply unit during inflation or deflation of the air springs.
The silencer comprises two plastic molded cans bonded together and contains two blocks of silencing foam. A pipe connection is molded onto each end of the silencer and provide for the attachment of the exhaust air to atmosphere pipe and the exhaust air pipe from the air supply unit.
A secondary chamber, located around the outside of the exhaust chamber forms the silencer for the inlet air. Pipe connections are molded onto each end of the intake silencer and provide for the attachment of the air inlet pipe from the inlet air filter and the air inlet pipe to the air supply unit. The intake air silencer is a hollow chamber with no noise reduction foam filling.
The air intake filter is connected via a pipe to the intake silencer chamber of the air silencer unit. The filter is located in the rear left hand corner of the body, away from possible sources of dirt and moisture.
The filter contains a foam element which removes particulate matter from the inlet air before it reaches the silencer or the air supply unit.

AIR HARNESS









The air harness comprises ten separate nylon pipes which are connected between the system components with Voss connectors. The pipes have the following diameters:





If a pipe becomes damaged, an in-line connector is available for repair purposes. The pipes are secured to the body and the chassis with a number of plastic clips.

CONTROL DIAGRAM

NOTE:
A = Hardwired