Part 4

Vehicle Dynamic Suspension (Part 4)

SPECIAL MODES

Door Open Functionality
If one or more of the vehicle doors are opened during a height change when the vehicle is stationary, the air suspension control module will restrict further height change. The door open signal is transmitted by the GEM (generic electronic module) on the K bus to the instrument cluster gateway and from the cluster is transmitted on the high speed CAN bus and received by the air suspension control module. This keeps the vehicle level to the set height when a door opens to allow for changes in loading conditions.

The LED on the air suspension LED display for the target mode height will remain illuminated and the height change LED will flash.

If all of the doors are closed within 90 seconds, the height change will resume. If the 90 second period is exceeded and all of the doors are not closed, the height change will be canceled. The mode LEDs showing the previously selected height and the target height will be illuminated. The mode height change can be reselected by operating the rotary switch, however, if the vehicle is driven at speed of more than 5 mph (8 km/h) the control module will continue to raise or lower the vehicle to the target mode height.

Extended Mode
If the air suspension control module senses, via the height sensors, that the vehicle has become grounded, the air suspension control module automatically increases the mass of air in the air springs to raise the vehicle clear of the obstruction. Extended mode is activated automatically and cannot be selected manually.

When the air suspension control module has activated the extended mode, the off-road mode lamp will flash if the suspension is above off-road mode height. The off-road mode and on-road mode lamps will flash if the suspension is between off-road mode and on-road mode heights. The on-road mode and access mode lamps will flash if the suspension is between on-road mode and access mode. A message will also be displayed in the message center.

To exit the extended mode, press the air suspension switch briefly in the up or down position or alternatively drive the vehicle at a speed of more than 12.5 mph (20 km/h).

Additional Lift in Extended Mode
When extended mode has been invoked and the automatic lifting of the vehicle is complete, the driver can request an additional lift of the vehicle. This can be particularly useful when extended mode has been activated on soft surfaces.

The additional lift can be requested once the height change LED has extinguished. Press and hold the air suspension switch in the up position for 3 seconds whilst simultaneously depressing the brake pedal. A chime from the instrument cluster will sound to confirm that the request has been accepted. The height change LED will be illuminated while the vehicle is being lifted.

Suspension Prevented From Moving
If the air suspension control module is attempting to change the suspension height and it detects that the suspension is prevented from moving, the control module will stop all suspension movement. This can be caused by jacking the vehicle, attempting to lower the vehicle onto an object or raising the vehicle against an obstruction.

The air suspension switch lamps operate as described for extended mode and the same message is displayed in the message center. To re-start the air suspension system operating, press the air suspension switch briefly in the up or down position or drive the vehicle at a speed of more than 12.5 mph (20 km/h).

Periodic Re-levelling
When the vehicle is parked, the air suspension control module 'wakes up' two hours after the ignition was last switched off and then once every six hours. The vehicle height is checked and if the vehicle is not level within a pre-set tolerance, small downwards height adjustments may be made automatically.

Transportation Mode
Transportation mode is a factory set mode which locks the suspension to enable the vehicle to be safely lashed to a transporter. The suspension transportation mode is automatically set when the vehicle is configured for transportation mode using T4. Transportation mode also affects other vehicle systems which are inhibited or restricted to a minimal functionality
When the ignition switch is switched off, the vehicle will be lowered onto the bump stops. This ensures that the securing straps do not become loose should air leak from the air springs.

When transportation mode is active, the off-road, access and hold switches are disabled. Periodic re-levelling is also disabled.

When the engine is started, the air suspension control module will cause the vehicle to rise to a height of -20mm to allow sufficient ground clearance for the vehicle to be loaded. While the height is changing, all the LEDs in the air suspension control switch will flash and a chime will be emitted by the instrument cluster. When the height of -20mm is reached, all the LEDs will illuminate continuously and the chime will stop.

When the engine is switched off, the air suspension control module will cause the vehicle to lower to a height of -60mm to allow the vehicle to be strapped down. While the height is changing, all the LEDs in the air suspension control switch will flash and a chime will be emitted by the instrument cluster. When the height of -60mm is reached, all the LEDs will illuminate continuously and the chime will stop.

Calibration Mode
This mode is used when the air suspension control module has been replaced or a height sensor or suspension component has been dismantled or replaced.

These conditions apply when the vehicle is in calibration mode:
^ The ride height is set to tight tolerance
^ Fault reaction to Vehicle Identification Number (VIN) mismatch with the Car Configuration File (CCF) is disabled
^ The raise, lower, access and hold switches are disabled
^ System is controlled to on-road height only.

AIR SUSPENSION COMPONENTS
The air suspension comprises:
^ 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 which is located adjacent to the CJB (central junction box), behind the instrument panel. The control module is housed in a plastic bracket attached to the 'A' pillar.

Valve Blocks

Front and Rear Valve Blocks (Part 1):

Front and Rear Valve Blocks (Part 2):

Reservoir Valve Block (Part 1):

Reservoir Valve Block (Part 2):

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 DTCs 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 pulled 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 pulled 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 pulled 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 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. When energized, the solenoid moves the valve spool 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 17.5 bar gage (254 psi).

This graph shows nominal pressure values against sensor output voltage.

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

Valve Block Solenoid Specifications:

Air Supply Unit (Part 1):

Air Supply Unit (Part 2):

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 these 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 deenergized, 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 under air suspension control module.

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.

This table shows the control module operating parameters for the differing air supply unit functions and the allowed motor operating temperatures.

Motor Operating Temperatures

Motor Operating Temperatures:

This graph shows motor temperature sensor resistance values against given temperatures.

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

This 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 17.5 bar gage (254 psi).

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 the silencers 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.

This table shows the control module operating parameters for the differing air supply unit functions and the allowed compressor cylinder head operating temperatures.

Compressor Cylinder Head Operating Temperatures

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 end of the air dryer unit 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 psi).

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.

Air Supply Unit Specifications:

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 under Air Suspension Control.

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 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 10.2 liters (622 cu. inch). The nominal working pressure of the reservoir is 14.4 to 15.5 bar gage (209 to 224 psi), with a maximum pressure of 22 bar gage (319 psi).

Height Sensors

Height Sensors (Part 1):

Height Sensors (Part 2):

A height sensor is fitted in each corner of the vehicle to monitor the ride height of the vehicle. The sensors are mounted on the front and rear subframes, with a mechanical link to the suspension lower arms. There are four different types of sensor fitted.

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

If a height sensor is removed from its mounting position for servicing or replacement, T4 must be used to recalibrate the system. Calibration will also be required if the suspension arm to which the sensor is connected is removed or replaced or if a replacement drop link is fitted.

A calibration routine is performed using T4 to read the position of each corner of the vehicle and record the settings in the control module 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.

The height sensors are attached to brackets on the subframes and are connected to the lower arms by links. The links allow articulation of the arm to allow for suspension travel. Each sensor is connected by a six pin multiplug.

The front and rear sensor drop links are serviceable items.

Each sensor comprises a sensor body which contains a single track rotary potentiometer, a lever arm and a drop link. The sensor is supplied with a reference voltage from the air suspension control module which measures the returned voltage to determine the sensor arm position. On the front height sensors the voltage decreases as the vehicle height increases. On the rear sensors the voltage increases as the vehicle height increases.

The sensors can be checked by applying 5V across the positive and negative terminals and measuring output signal which should be a nominal 57 mV ± 3% per degree of sensor arm movement.

This graph shows the vehicle height displacement from normal against output voltage for the front height sensors^The (blue) center line represents the "nominal" condition but depending on tolerances, the actual line may lie anywhere between the (green) upper and (red) lower lines.

Front Height Sensor

Front Height Sensor (Part 1):

Front Height Sensor (Part 2):

This graph shows the vehicle height displacement from normal against output voltage for the rear height sensors^The (blue) center line represents the "nominal" condition but depending on tolerances, the actual line may lie anywhere between the (green) upper and (red) lower lines.

Rear Height Sensor