Land Rover Defender: Operation

CHASSIS CONTROL MODULE

The CHCM uses a combination of information from other system modules and data from the accelerometers and suspension height sensors to measure the vehicle and suspension states and driver inputs. Using this information, the CHCM applies algorithms to control the shock absorbers for the current driving conditions.

The CHCM receives the following signals over FlexRay from the stated system components:

• Brake Pressure - Anti-lock Brake System (ABS) control module
• Vehicle Speed - ABS control module
• Front Left Wheel Speed - ABS control module
• Front Right Wheel Speed - ABS control module
• Rear Left Wheel Speed - ABS control module
• Rear Right Wheel Speed - ABS control module
• Roll Stability Control Mode - ABS control module
• Steering Wheel Angle Speed - ABS control module
• Steering Wheel Angle Status - ABS control module
• Lateral Acceleration - ABS module
• Engine Speed - PCM
• Engine Torque - PCM
• Gear Position Target - Transmission Control Module (TCM)
• Torque Converter Slip - TCMPower Mode (Ignition Signal) - Body Control
• Module/Gateway Module (BCM/GWM)
• Terrain Mode Requested - BCM/GWM

The CHCM also outputs information on the High Speed (HS) Controller Area Network (CAN) buses and Flexray for use by other systems as follows:

• Fault Message
• Terrain Mode Change Status.

The CHCM monitors the input signals and operates the shock absorber solenoids. The input signals are used in control functions and a force required for each shock absorber, for each function, is calculated. An arbitrator monitors the force requirements from each function and apportions a force to a shock absorber. The force is converted to the appropriate current and sent to the shock absorber.

The control functions are as follows:

• Body Control - Uses CAN and accelerometer inputs. Calculates road induced body motions 100 times a second and sets each shock absorber to the appropriate level to maintain a flat and level body.
• Roll Rate Control - Uses CAN inputs. Predicts vehicle roll rate due to driver steering inputs 100 times a second and increases damping to reduce roll rate.
• Pitch Rate Control - Uses CAN inputs. Predicts vehicle pitch rate due to driver accelerate and brake inputs 100 times a second and increases damping to reduce pitch rate.
• Bump Rebound Control - Uses suspension height sensor inputs. Monitors the position of the wheel 500 times a second and increases the damping rate as the shock absorber approaches the end of its travel.
• Wheel Hop Control - Uses suspension height sensor and CAN inputs. Monitors the position of the wheel 500 times a second and detects when the wheel begins to vibrate at its natural frequency and increases the damping to reduce vertical wheel motion.

Under normal road conditions when the vehicle is stationary in Power Mode 7 (Engine running), the shock absorbers are set to the firm condition to reduce power consumption.

The CHCM receives power supply through a relay and fuse in the Rear Junction Box (RJB). The relay remains energized for a period of time after the ignition is Off. This allows the CHCM to record and store any Diagnostic Trouble Code(s) (DTC) relating to adaptive damping system faults. The CHCM receives ignition signal from the BCM /GWM.

AIR SUSPENSION SYSTEM OPERATION

NOTES:

• The suspension adjusts if the vehicle's doors are open, but the vehicle may not lower to its minimum setting.
• A time delay may be evident before the vehicle reacts to a suspension height request, through the buttons.

  The vehicle's systems need to be configured before each height adjustment.

Under normal operating conditions, the CHCM keeps the vehicle level at the 'current' ride height. The incoming height signals from the sensors are passed through filters to remove irregular signals produced by road noise or other irregularities. When the vehicle is stationary or a height change is in progress, the signals are passed through a 'fast' filter. The 'fast filter' tracks the true rate of change of height. When the vehicle is moving, the signals are passed through a 'slow' filter. The 'slow' filtered signals remove almost all road noise from the signals and output a true long term average for each corner height. The 'slow' filtered signals cannot be used to respond quickly during height changes.

The CHCM monitors each corner height signal using the fast filtered signals if the vehicle is stationary or the slow filtered signals if the vehicle is moving. If the height remains in a 'dead band' which is +- 9 mm from the target height, the control module does not implement any height adjustment changes. When the CHCM detects that a corner is outside of the 'dead band', the CHCM operates the compressor and/or the valves to move that corner back into the target height.

RIDE HEIGHT TOLERANCE CONTROL

The CHCM has 2 ride height tolerance bands: normal tolerance and tight tolerance.

The CHCM considers the vehicle to be at target height if the current height is within the appropriate tolerance band.

Height adjustments are not made until the vehicle height falls outside of the tolerance band for a pre-determined time.

The time period is different depending on if the vehicle is moving or stationary.

The tolerance bands are as follows:

• Normal +- 9 mm (0.35 in)
• Tight +- 3 mm (0.11 in).

The tight tolerance band is set by the JLR approved diagnostic system and only used in the following conditions:

1. Height calibration
2. Headlamp calibration suspension set-up
3. Suspension geometry set-up

The tight tolerance band also can be activated by the following procedure:

1. Start the engine.
2. Set the suspension to normal height.
3. Open the driver door.
4. Press the brake pedal lightly 3 times in quick succession.
5. Close the driver door within 10 seconds of the first brake pedal press.

If the procedure is successful, the Instrument Panel Cluster Control Module (IPC) emits 2 soft chimes about 1 second after the driver door is closed. Thereafter the IPC emits 2 soft chimes each time the driver door is closed to confirm that tight tolerance mode is still active.

The tight tolerance mode cancels when the engine is turned off or the vehicle speed exceeds 8 km/h (5 mph).

AIR SUSPENSION SWITCHPACK

The driver can manually select, using the air suspension switch, 1 of 4 ride states:

• NORMAL - this height is the normal operating height of the vehicle
• OFF-ROAD - this is higher than the on-road height and provides improved ground clearance, approach, departure and break-over angles up to speeds of 80 km/h (50 mph).
• ACCESS - this is lower than the on-road height and provides easier access, agrees and the vehicle loading.
• Locked at access - this allows the vehicle to be driven at the access height at speeds up to 40 km/h (25 mph) to provide increased roof clearance in low car parks, for example.

Vehicle height changes are restricted if the CHCM receives a 'Door Open' signal and the speed is less than 8 km/h (5 mph).

A complete vehicle transit mode is available but is only selectable using the Land Rover approved diagnostic system.

When this mode is active most vehicle systems, in addition to the air suspension, are inhibited or restricted to a minimal functionality. In this mode the air suspension is set to the transit mode.

If the CHCM senses that the vehicle has grounded and lost traction, the CHCM can temporarily raise the vehicle to maximize the available traction.

This is known as extended mode and to be indicated to the driver:

• by the height indicators flashing in the ICIMA
• and an 'EXTENDED MODE' message is displayed in the IPC.

If a fault is detected by the CHCM, the control module reduces the system functionality dependent on the type and severity of the fault. The control module also stores a fault code which can be retrieved using the JLR approved diagnostic system. If a severe fault occurs, the control module attempts to put the vehicle in a safe condition. A fault is relayed to the driver by the IPC message center and an audible warning emitted from the IPC.

All information messages are to be displayed for 4 seconds.

Normal Height

This is the normal ride height for the vehicle.

Off-Road Mode

Off-road height can be selected from normal height by pressing up on the raise switch at any speed up to 70 km/h (43 mph). The message center displays OFF-ROAD HEIGHT SELECTED.

The Off-road height is dependent upon vehicle speed. The Off-road height selection is confirmed on the IDMA.

Off-Road 1 height is 40 mm (1.57 in) above normal height up to 80 km/h (50 mph).

Off-Road 2 height is 75 mm (2.95 in) above normal height up to 50 km/h (31 mph).

The suspension height can change automatically between these heights.

Off-Road 2 can be selected when at Off-Road 1 height by pressing up on the raise switch when traveling less than 40 km/h (25 mph). To select normal height, press down on the lower switch or increase the speed above 80 km/h (50 mph).

Access Height

Access height provides easier entry, exit and loading of the vehicle.

Access height can be selected at any vehicle speed. When access height is selected, the response of the air suspension system depends on the vehicle speed.

• If the vehicle speed is more than 20 km/h (12.5 mph), the CHCM wait for up to 1 minute for the vehicle speed to be reduced. The access mode indicator and the lowering indicator are flash while the CHCM waits for the vehicle speed to be reduced; the Normal height indicator remains illuminated. If the vehicle speed is not reduced sufficiently, the access height request is to be canceled after a minute.
• If the vehicle speed is less than 20 km/h (12.5 mph), the CHCM lower the suspension to a part lowered height and remains at this height for up to 1 minute. The normal height indicator extinguishes as the CHCM lowers the suspension to the part lowered height. The access height indicator and the lowering indicator illuminate. When part lowered is reached, the lowering indicator flashes. If the vehicle speed is not reduced to less than 8 km/h (5 mph) in the 1 minute period, the access height request is canceled.
• If the vehicle speed is less than 8 km/h (5 mph), the suspension is lowered to access height immediately. The access height indicator and the lowering indicator illuminates. When the access height is reached, the lowering indicator is extinguished.

Access height may be selected up to 60 seconds after the ignition is turned off, provided that the driver's door has not been opened within this time.

The suspension will automatically rise from access height when the vehicle speed exceeds 7km/h (4.3 mph) for 3s or 15 km/h (9.3 mph).

Locked At Access Height

Locking the suspension at access height allows the vehicle to be driven at low speeds with the suspension locked at the access height. This allows the vehicle to be driven in low car park with increased roof clearance.

When the vehicle is at access height and traveling speed is less than 35 km/h (22 mph), press down on the lower switch for longer than 1 second. The system lock indicator illuminates and SUSPENSION LOCKED AT ACCESS HEIGHT is displayed in the message center.

To cancel this mode, press up on the raise/lower switch for longer than 1second or increase the speed to 40 km/h (24 mph).

Automatic Height Change Warnings

When the suspension is locked at access height, the CHCM changes the suspension height automatically when the vehicle speed exceeds 40 km/h (24 mph). The control module issues a warning to advise the driver that the vehicle is approaching the speed threshold when the speed reaches 35 km/h (22 mph). The IPC sounder emits a chime, a message is displayed in the message center and the normal height indicator and the raising indicator flashes.

The warning is removed when the vehicle speed is reduced.

Auto Access Height

Auto access height can be enabled or disabled, through the vehicle settings/set-up in the message center configuration menus.

If auto access height is enabled, the suspension to be lowered automatically to allow for easier access, when the vehicle is parked.

The following conditions are to be apply:

• The suspension has to be at the normal height setting.
• The transmission has to be engaged in high range.
• The Terrain response system has to be set to the Automatic setting, General program, Dynamic program or the Grass/Gravel/Snow program.

NOTE: Auto access height operates more quickly and smoothly if the Electric Park Brake (EPB) is applied and the brake pedal is completely released.

Auto access height will initially lower the suspension up to 15 mm (0.59 in) below the normal height setting, during any of the following events:

• When the vehicle is stationary and any of the front or second row (not third row) occupied seatbelts are unbuckled.
• The ignition is switched off.

When a door is subsequently opened, after the initial lowering of the suspension, then auto access height lowers the suspension to the lowest setting. The lowest setting is 40 mm (1.57 in) below the normal height setting.

NOTE: If a door is not subsequently opened, after the initial lowering of the suspension and the vehicle's speed exceeds 40 km/h (25 mph), then the suspension is return to the normal height setting.

Auto access height lowers the suspension to 30 to 35 mm (1.18 to 1.37 in) below the normal height setting, if a door is opened before any the following events occur:

• Before any of the occupied seatbelts are unbuckled.
• Before the ignition is switched off.

The air suspension system lowering button can be pressed to lower the vehicle to the full access height, if the air suspension system is still active.

Normal driving is automatically return the suspension from access height to the previous setting. Normal height can be selected by pressing the up arrow on the suspension system's raise/lower switch.

Auto access height can be activated up to 90 seconds after the vehicle becomes stationary.

Auto access height only operates when for each time the vehicle becomes stationary. If further operations are required while at the same location, use the message center menus to disable and then enable the feature again. Alternatively, drive the vehicle at a speed above 7 km/h (4 mph) for 3 seconds or at a speed of more than 15 km/h (9 mph).

NOTE: This also applies in the event that the vehicle is stationary for more than 90 seconds without activating auto access height. If a door is opened after 90 seconds, then an 'Auto Access timed out' message is displayed in the message center.

Auto access height does not operate in the following conditions:

• The suspension has entered into extended mode.
• The vehicle is on a steep incline/decline, or on a very uneven surface.
• There are not sufficient air reserves in the air suspension system, to lower and raise the suspension. In this event, an 'Auto Access temporarily not available' message is displayed in the message center, when a door is next opened.

REAR HEIGHT ADJUST

NOTE: The rear switchpack is disabled when the tailgate is closed.

This feature allows the user to alter the vehicle rear end ride height, using the switchpack in the luggage compartment to allow easier luggage compartment loading. The user can also alter the rear end ride height using the smart key.

The adjustable rear height settings are also beneficial when hitching and un-hitching trailers.

CAUTION: Care should be taken with all suspension height changes, especially when a trailer is attached to the vehicle.

Incorrect suspension adjustments can result in serious damage to the vehicle.

To operate the suspension's rear height adjust through the rear switchpack, unlock the vehicle and open the tailgate.

Operate as follows:

• Press and hold the switch (1) to lower the rear suspension.
• Press and hold the switch (2) to raise the rear suspension.
• Simultaneously press and hold both switches to set the rear suspension to the normal height setting.

Rear height settings at the tow hitch:

• To drop 60 mm (2.36 in) for loading the luggage compartment
• To rise 90 mm (3.54 in) into assist hitching or unhitching.

PERIODIC WAKE-UP MODE

When the vehicle is parked, the CHCM 'wakes up' 2 hours after the ignition was last switched OFF and then every 24 hours thereafter. The vehicle height is checked and if the vehicle is not level within a pre-set tolerance, small downward height adjustments may be made automatically.

EXTENDED MODES

Lower Inhibit

Lower inhibit is a reactive mode invoked when the when rate of vehicle lowering is below a predefined threshold for a predefined time during a downward height change. Lower inhibit is normally invoked when the vehicle is lowered onto an obstacle.

Belly-Out

Belly-Out is a pro-active mode invoked when the following conditions are satisfied, vehicle moving and speed is below 20 km/h (12.5 mph). Traction activity is induced on axle pairs for fixed period of time and wheel heights above a predetermined threshold on coinciding axle pairs for the same fixed period of time. Belly-Out is normally invoked under the following condition, vehicle is attempting to move and with low levels of traction and supported by an obstacle.

If the vehicle body is raised, for example by a jack, or grounded in severe off-road conditions, the system may automatically enter Extended Mode. Indicators in the raise/lower switch flash and the message center displays SUSPENSION IN EXTENDED MODE.

The suspension can rise automatically to assist in clearing the obstacle. When extended mode height is achieved, the driver may request additional lifting if required. This is achieved by pressing up and holding the raise switch for longer than 3 seconds while pressing the brake pedal.

Extended mode is canceled by pressing down on the raise/lower switch or when the vehicle speed confirms that the body is no longer lifted or grounded.

Extended mode cannot be selected manually.

TRANSIT MODE

When transit mode is active, the air suspension switches are disabled. Periodic re-leveling is also disabled.

When the engine is started, the CHCM causes the vehicle to rise allowing sufficient ground clearance for the vehicle to be loaded. While the height changes, all the indicators in the air suspension control switch flash and a chime is emitted by the Integrated Control Panel (ICP). When the correct height reached, all the indicators illuminate continuously and the chime stops.

When the engine is switched off, the CHCM causes the vehicle to lower, allow the vehicle to be strapped down. While the height changes, all the indicators in the air suspension control switch are flash. When the low height is reached, all the indicators illuminate continuously.

CALIBRATION MODE

This mode is used when the CHCM is replaced or a height sensor or suspension component are dismantled or replaced.

The following conditions apply when the vehicle is in calibration mode:

• The ride height is set to tight tolerance
• Fault reaction to Vehicle Identification Number (VIN) mis-match with the Car Configuration File (CCF) is disabled
• The raise, lower, access and hold switches are disabled
• Message "Air suspension not in customer mode" is displayed in the Instrument Panel Cluster (IPC).

REMOTE OPERATION

1. Approach lamp switch
2. Tailgate opener switch
3. Unlock switch
4. Lock switch

WARNING: The smart key can be operated from inside or outside of the vehicle. Make sure that the smart key is always kept safely out of children's reach, to avoid serious injury or death.

The switches on the smart key may be used to operate the air suspension system, allowing the vehicle to be raised or lowered remotely. This may be useful in attaching a trailer or loading the vehicle.

To change the suspension height using the smart key, the vehicle must be stationary, all the doors closed and the hazard warning lamps switched on.

Operate the smart key as follows:

• To lower the vehicle suspension, press and hold the switches 1 and 2 simultaneously.
• To raise the vehicle suspension, press and hold the switches 1 and 3 simultaneously.
• To return the vehicle to normal height, press and hold the switches 1 and 4 simultaneously.

The indicator lamps, on the electronic air suspension controls, indicate the current status of the rear suspension, after adjustment. If the rear suspension is currently above normal height, then both the normal height and off-road height indicator lamps illuminate. If the rear suspension is currently below normal height, both the normal height and access height indicator lamps illuminate.

LEAK DETECTION

Leak detection can be completed using a JLR approved leak detection spray.

If the vehicle appears to be leaking, perform a leak check on all aspects of the system. For example, air spring pipe fittings and the associated connections on the valve blocks, air springs and reservoir. Failure to correctly diagnose leakage results in unnecessary exchange of serviceable components and recurrence of the original problem.

SYSTEM INHIBITS

A number of conditions exist where a change in ride height is undesirable. To counter this, the CHCM is programed with a number of system inhibits. If any of the conditions detailed below exist, the CHCM suspends height changes and height corrections.

System Pressure

The compressor will not start if the system pressure is greater than 4 bar.

Compressor Temperature

A temperature sensor is located within the compressor to prevent overheating. If the temperature of the compressor cylinder head rises above pre-set limits, the CHCM will inhibit the compressor operation.

Cornering

If the CHCM 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 CHCM receives a message from Restraints Control Module (RCM) - incorporating the yaw rate lateral acceleration sensor over the Flexray from the Anti-Lock Brake System Control Module (ABS) for the applied cornering force.

Rapid Acceleration

If the CHCM 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 CHCM from a vehicle speed signal received through the HS CAN Underbody (UN) systems bus.

Rapid Deceleration

If the CHCM 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 control module from a vehicle speed signal received through the HS CAN Underbody (UN) systems bus.

Door Open

The CHCM 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. Door open status is ignored when the vehicle speed is above 8 km/h (5 mph).

HEIGHT SENSOR CALIBRATION

A calibration routine is performed using the diagnostic system to calculate the offset for each corner of the vehicle.

The offset is calculated from the relationship between the mechanical tolerances and the height sensor signals for each individual corner.

A calibration routine is performed using the JLR approved diagnostic equipment:

• to manually measure each corner of the vehicle
• to read the corresponding ECU heights for each corner of the vehicle
• to record the calculated height offsets into the CHCM memory.

When set, the calibration is not required to be performed unless:

• the CHCM is replaced
• the height sensor or its bracket is removed, disconnected or replaced
• the suspension arm to which the height sensor is connected is removed or replaced.

If the removed height sensor is subsequently reinstalled, the calibration procedure must be perform to make sure the integrity of the system.

If a replacement drop link is installed calibration is required.

The sensing element consists of an array of Hall effect devices arranged to measure the direction of the magnetic field of a small magnet attached to the end of the sensor shaft. As the sensor shaft rotates, so do the lines of magnetic flux from the magnet. The signals from the hall effect elements are processed by means of a dedicated integrated circuit to generate an output voltage that varies as the sensor shaft is rotated. The sensor has a measurement range of +- 40º around its nominal position and the nominal sensitivity is 57 mV/º of shaft rotation.

DIAGNOSTICS

The CHCM can store DTCs which can be retrieved using a JLR approved diagnostic system. The diagnostics information is obtained through the diagnostic connector which is located below the instrument panel, above the driver's foot pedals.

The diagnostic connector allows the exchange of information between the various control modules on the bus systems and the JLR approved diagnostic system. This allows the fast retrieval of diagnostic information and programming of certain functions using the JLR approved diagnostic system.

Fault Messages

The air suspension has 2 methods which can use to inform the driver of a fault in the air suspension system:

• The air suspension control switch indicators
• The Instrument Panel Cluster (IPC) message center.

If the CHCM suffers a major failure and there is no air suspension control, all the control switch indicators remain unlit.

If a fault occurs and the CHCM can determine the ride height and the vehicle is not above on-road height, a message appears in the message center. If the CHCM cannot determine the ride height, or the vehicle is above normal height and cannot be lowered, a message is displayed and accompanied with a maximum speed message.

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