Overview of Mk III Range Rover Independent Air Suspension

With the advent of the Mk III model in 2003, the most significant change in the suspension department was a switch to an all-independent suspension replacing the beam-axles used on all previous models. As usual when new technology is introduced in Range Rovers, the nay-sayers were out in force declaring that off-road performance would be ruined. In fact the reverse was achieved, thanks to several clever design elements.

The well-known benefits of an independent suspension in reduced unsprung weight and improved ride quality apply equally well off road. In addition, the Range Rover suspension designed uses very long A-arms that were design to maximize ground clearance and articulation.  Finally,  the cross-linking of the left and right air springs under off road conditions reproduces the ground-clearance enhancing action of a beam axle, while at the same time radically improving both traction and ride quality. An over view of the manual and automatic control of this new and unique system, and the benefits it bestows, are presented on the Range Rover suspension page.

The one thing Land Rover signally failed to do in designing the new system was to make it user-friendly  when failures occur in the field, far from the nearest dealer. All too easily, the vehicle's electronic brains intervene to prevent restoration of normal operation. Accordingly, just like the previous air suspended models, owners who actually use their vehicles off road have to resort to  knowledge that goes beyond the  shop manual when failures do occur. The purpose of these pages is to try and help fill this gap.

Mechanical Design

Both the front and the rear suspensions (and the rear differential) are mounted on subframes fabricated from tubular steel and bolted to the underside of the Range Rover's monocoque body.

The front suspension uses vertical MacPherson struts, incorporating the shocks or dampers and the air springs (instead of the usual coils) at the top end. (We can bet this is a nice expensive component to replace!!) The top end of the strut is mounted to the wheel well and the bottom end to the wheel hub. Horizontal location of the wheel hub is provided by two suspension arms that are positioned in an "A" configuration but are separate rather than being a single stamping as used on lesser vehicles. The front arm is termed a transverse link and the rear one is a compression link. A 30 mm (1.2 inch) diameter anti-roll bar has vertical links that attach directly to the MacPherson struts to harness the full travel of the suspension. Camber can be adjusted at the top mount of the MacPherson strut, and toe-in can be adjusted via the track rod ends.

The rear suspension is designed to be stronger for load carrying and towing, and to have more vertical travel than the front. It uses a double wishbone arrangement with the air spring positioned between the lower wishbone and the tubular steel subframe. A separate toe control arm in front of and between the upper and lower wishbones, in conjunction with ball joints where the hub mounts to the upper and lower wishbones, allows adjustment of wheel alignment for camber and toe-in using eccentric bolts.  A 23 mm anti-roll bar is attached by links to the lower A arm. The rear shocks (dampers) are a special monotube design by Bilstein.

Specifications

The shop manual gives the following figures for available front and rear wheel travel:

Height Settings and Modes

1. Access height -- 1.8 inches (40 mm) below standard height. If preselected prior to stopping, it will take effect when speed drops below 15 mph. If 'Hold' is selected while at access height, 'Crawl' mode is activated and speed can rise to 25 mph (40 km/h) before the vehicle will return to standard height.

2. Motorway -- 0.8 inch (20 mm) below standard; selected automatically when  speed is above 62 mph  for more than 30 seconds.

3. Standard Height -- default position used in normal around-town driving.

4. Off-Road -- raises the front 2.4 inches and the rear 2.0 inches above standard.

5. "Transportation Low" (selected by Testbook or equivalent) drops the vehicle 20 mm below "access" when the engine is off, for chaining to a transporter.

Access Height	Standard Mode	Off-Road Height
Photos of Murray James-Wallace's RR at Point Moore Lighthouse, Geraldton, Western Australia. Click on any image to see full-size version.

Manual and Automatic Height Controls
Two dashboard switches provide manual control of ride height settings. There is an up-down rotory control switch which allows manual selectionn of access, standard and off-road heights. The control switch has a "hold" button at the center of it, allowing the driver to hold the vehicle in standard height mode. Low profile /motorway setting cannot be nanually selected, but once the vehicle is at this height it can be held there by the "hold" switch. There is an additional switch on the driver's door that can be used to select access mode.

Dash controls for EAS: up-down rotary switch at lower right (with inhibit button in its center); LED indicators lower center.	Window sill mounted access height selector button at extreme top of photo. (Photos courtesy of  Murray James-Wallace).

Left-Right Cross-Linking
When the air suspension ECU senses wheel movements corresponding to off-road conditions, front and rear cross-linking solenoid valves are opened, allowing air to flow freely between left to right airbags, making for greatly increased ground contact force (and traction) on a drooping wheel, as well as a soft off-road ride.

Electronic Air Suspension Components and Failure Modes (Mk III)

Here we list the main components of the system as an aid in fault diagnosis, along with some notes on their failure modes.

• Air springs similar to those on large trucks, but with longer travel and air inlets at the top to allow air to be pumped in or exhausted under computer control. These develop slow leaks at top and bottom when old, or can blow out spontaneously when pierced by an off road obstacle.
• A compressed air tank of about 10 liter (2 1/2 US gallon) capacity, made of aluminum, is located under the right hand side of the vehicle. This is not likely to fail but could leak at the outlet, drain plug or pressure sensor plug.
  
• A pressure sensor is screwed into the rear of the air tank. In a typical piece of brilliant Land Rover design, if this sensor fails the whole air tank has to be replaced!!
  
• A compressor (housed in a sealed circular enclosure inside the spare wheel compartment under the rear loadspace) keeps system pressure between 9 and 13.7 bar (135 and 200 psi). . The compressor eventually wears out resulting in slow pumping -- if bad enough will cause fault mode when takes too long to reach pressure. The compressor incorporates a temperature sensor that is read by the ECU, which shuts off the compressor if it overheats. Failure of this sensor can cause the compressor to stop pumping. In the Mk III the electric driving the compressor can easily be replaced as a deparate part. There are manu conditions that inhibit operation fo the compressor; however failure of the motor to operate at all may mean a blown fuse or relay.
  
• An air dryer located in the compressor housing prevents accumulation of water in the air tank. Exhausted air flows through it in reverse to recharge its desiccant. Saturation of desiccant could result in accumulation of water in the compressed air tank.
• A solenoid operated exhaust pilot valve for letting air out of the springs is mounted to the air dryer. An air operated pressure limiting valve is also located here to prevent system over-pressure. This valve also opens when air is being exhausted from the springs.
  
• A valve block (mounted on the forward end of the air tank) includes five solenoid valves. One "corner" valve for each spring controls air flow to and from the spring in question via the cross-link valves (see below). A "reservoir" valve regulates air flow between the reservoir and the valve block. The valve block is is the most expensive component in the system. Eventually the valves start leaking and its internal O-rings need to be replaced -- if this does not work the entire block has to be replaced.
• Cross linking valves (one at the front and one at the rear): when activated these shut off external air flow but allow flow between left and right springs. In the normal or deactivated position, air is free to flow to or from each individual spring via the main valve block depending on the positions of the corner and reservoir valves.
  
• A height sensor (using a Hall effect sensor rather than the potentiometer used in older models) is attached to each suspension radius arm to sense the vertical position of each wheel. Each corner sensor is slightly different, and models with xenon headlights have a second circuit in the right hand sensors which is used for leveling the lights. Any sensor can fail leading to inability to level the vehicle. Disconnected sensor can lead to suspension stuck at one height.
• A ride height control (rotory) switch on the dash allows the driver to set ride height manually. Another ride height switch is provided on the driver's door for access mode only. Failure of the switches can prevent automatic height changes.
• A hold switch on the dash allows the driver to lock the suspension at any height setting. Powered by fuse F17 in BeCM fuse box. Failure can prevent automatic height changes.
• An ECU under the left side of the dash receives signals from the wheel height sensors, pressure sensor, compressor temperature sensor, control switches  and the Body Control Unit (BCU) and sends signals to the various solenoid valves and the compressor to control the air flow to and from each air spring. The ECU is Powered from a fuse under hood.
  
• The air lines connecting the various components are made of color coded nylon; right hand pipes are yellow and left hand pipes are black.  They are all metric sizes, with outside diameters of 6 mm for most lines. Leaks in lines can cause anything from marginal operation to catastrophic failure. However cutting of individual lines unlikely; slow leaks at connections to valve block or springs most likely.
Unusually tall and flexible bump stops are provided to act as surrogate springs to "get you home" even when the system fails completely. Worn or dislocated bump stops result in suspension knock or VERY hard ride in case of EAS failure.

ECU Operation & Reactions to Faults

See separate page on  the EAS ECU's reaction to different types of faults that might occur in the field.
Also see the EAS Field Recovery page dealing with the earlier models; many of the same techniques apply.

Page last updated August 8, 2004



Return to Repair Operation Details
Return to Rangerovers.net Main Page