Part 3

Vehicle Dynamic Suspension

AIR SUSPENSION COMPONENTS
The air suspension comprises the following:
- Two front struts incorporating air springs
- Two rear air springs
- Front and rear valve blocks
- Reservoir valve block incorporating a pressure sensor
- An air reservoir
- Four height sensors
- Air supply unit
- Air suspension control module
- Air supply pipes
- Air suspension control switch.
The air suspension system is controlled by the air suspension control module. The control module is located in the RH (right-hand) rear quarter panel.

Valve Blocks

Front and Rear Valve Blocks

Reservoir Valve Block

Front and Rear Valve Blocks
The front and rear 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 and may result in misleading DTC (diagnostic trouble code)'s being set.
The front valve block is attached to a bracket at the rear of the right hand front wheel arch, behind the wheel arch liner. The valve block has three attachment lugs which are fitted with isolation rubber mounts. The rubber mounts locate in 'V' shaped slots in the bracket. 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 attached to a bracket at the top of the right hand rear wheel arch, behind the wheel arch liner and adjacent to the fuel filler pipe. The valve block has three attachment lugs which are fitted with isolation rubber mounts which locate in the bracket in three slotted holes. 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.
Reservoir Valve Block
The four way reservoir valve block is located in the air supply unit sealed housing. The valve block is attached to a bracket at the rear of the air supply unit on three attachment lugs which are fitted with isolation rubber mounts. The isolation rubber mounts locate in the 'V' shaped slots in the bracket and are pushed downwards into positive location in the slots.
The valve block controls the storage and distribution of air from the air supply unit and the reservoir and contains an integral system pressure sensor.
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 block 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 air supply to and from the reservoir. When energized, the solenoid opens the valve 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 14.5 bar gage (210 lbf/in2).
The following graph shows nominal pressure values against sensor output voltage.

Removal of the reservoir valve block will require full depressurization of the reservoir. The valve block is a non-serviceable item and should not be disassembled other than for replacement of the pressure sensor.

The air supply unit fitted from 2006MY is an improved unit providing quieter operation. Two silencer units are incorporated into the unit assembly to reduce operating noise.
The air supply unit is located in a housing which is mounted in the spare wheel well and secured with four bolts into threaded inserts to the vehicle floorpan. The unit is isolated from the vehicle body via four rubber isolation mounts.
The reservoir valve block is also located within the housing on a separate bracket at the rear of the unit.
The unit is connected to the system via a single air pipe to the reservoir valve block. Three air pipes from the reservoir valve block pass through an aperture in the unit housing and through a grommet in the wheel well. It is important to ensure that this grommet is not disturbed and correctly installed. Incorrect fitment will allow water to enter the wheel well leading to possible damage to and failure of the air supply unit.
The unit comprises a piston compressor, a 12V electric motor, a solenoid operated exhaust pilot valve, a pressure relief valve, an air dryer unit and two silencers.
The electric motor, compressor, air dryer and pressure limiting and exhaust valve are mounted on a frame which in turn is mounted on flexible rubber mountings to reduce operating noise. The unit is mounted on a pressed base plate which is located on the floor of the wheel well. The unit is protected by a pressed cover which is lined with an insulating foam further limiting the operating noise.
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. 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.

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 Printed Circuit Board (PCB) assembly. The sensor is connected to the air suspension control module which monitors the motor temperature and can suspend motor operation if the operating thresholds are exceeded.
The following table shows the control module operating parameters for the differing air supply unit functions and the allowed motor operating temperatures.

The following graph shows motor temperature sensor resistance values against given temperatures.

NOTE:
This graph is also applicable for the compressor cylinder head temperature sensor.

The following graph shows air suspension control module output voltages against motor temperature sensor temperatures.

NOTE:
This graph is also applicable for the compressor cylinder head temperature sensor.

Compressor
The compressor is used to supply air pressure to the air suspension reservoir. The air suspension control module monitors the pressure within the reservoir and, when the engine is running, maintains a pressure of 14.5 bar gage (210 lbf/in2).
The compressor comprises a motor driven connecting rod and piston which operate in a cylinder with a separate 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 the delivery valve through the air dryer and into the system.
The cylinder head is fitted with a temperature sensor. The sensor is connected to the air suspension control module which monitors the cylinder temperature and can suspend motor and compressor operation if an overheat condition occurs.
The following table shows the control module operating parameters for the differing air supply unit functions and the allowed compressor cylinder head operating temperatures.

Refer to the motor temperature sensor graph for compressor cylinder head temperature sensor resistance values and the air suspension control module output voltage / temperature sensor graph.
Air Dryer
Attached to the compressor is the air dryer which contains a Desiccant for removing moisture from the compressed air. Pressurized air is passed through the air dryer which removes any moisture in the compressed air before it is passed into the reservoir and/or the system.
When the air springs are deflated, the exhaust air also passes through the air dryer, removing the moisture from the unit and regenerating the Desiccant.
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, freezing can occur resulting in poor system operation or component malfunction or failure.
Pilot Exhaust Valve
Attached to the cylinder head is a solenoid operated exhaust pilot valve. This valve is opened when the air springs are to be deflated.
The pilot exhaust valve is connected to the air delivery gallery, downstream of the air dryer. The pilot valve, when opened, operates the compressor exhaust valve allowing the air springs to be deflated.
When the solenoid is energized, pilot air moves the exhaust valve plunger, allowing pressurized air from the air springs and/or the reservoir to pass through the air dryer to atmosphere.
Exhaust Valve
The exhaust valve operates when the pilot exhaust valve is opened, allowing air returning from the air springs and/or the reservoir to be exhausted quickly.
The pilot exhaust valve also provides the system pressure relief function which protects the air springs from over inflation. The valve is pneumatically operated, responding to air pressure applied to it to overcome pressure from its internal spring. 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 22 to 27 bar gage (319 to 391 lbf/in2).
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 with respect to atmosphere. This protects the air spring by ensuring it can still 'roll' over the piston without creasing.

NOTE:
Resistance values will vary with coil temperature. Resistance of test leads must be measured before any readings are taken. Resistance value of the test leads must be subtracted from final solenoid resistance value.
There are a number of conditions that will inhibit operation of the air suspension compressor. It is vitally important that these inhibits are not confused with a system malfunction. A full list of compressor inhibits is contained in the Air Suspension Control section.

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 located under the RH (right-hand) sill of the vehicle and is fabricated from steel and secured with four bolts to the underside of the vehicle.
The reservoir supplies pressurized air to the four air springs, via the valve blocks, to enable the air suspension system to carry out ride height changes.
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 9.5 liters (580 in3). The nominal working pressure of the reservoir is 14.5 bar gage (210 lbf/in2), with a maximum pressure of 22 bar gage (319 lbf/in2).