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Range Rover pages Air Suspension |
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Air suspension was fitted to the later Classics and a very similar system was fitted to the P38A. The air suspension system seems to be one of the main areas for faults and thus frustration amongst Range Rover owners. My own vehicle does not have air suspension, but for the benefit of others I have made the following notes whilst attending one of the Range Rover Register training courses and offer them by way of general information. No guarantee of accuracy is implied. This page is intended to show how it works, or at least how it should work! Consult the workshop manual first. Air Suspension Schematic Guide
Compressed air passes to the air dryer (3) where moisture is removed as it flows through the dryer desiccant. The desiccant. in the lower portion of the dryer becomes wet. Dried air passes through a non-return valve NRV1 to the reservoir (4). The three non-return valves (6) ensure correct air flow. They also prevent loss of spring pressure if total loss of reservoir pressure occurs. The pressure switch (5) maintains system pressure between set limits by switching on and off the compressor via an ECU controlled relay. For air to be admitted to an air spring (10), the inlet valve (7) must be energised together with the relevant air spring solenoid valve (9). For air to be exhausted from an air spring, the exhaust valve (8) must be energised together with the relevant air spring solenoid valve. The solenoid diaphragm valve (12) ensures that all air exhausted to atmosphere passes through the dryer, taking with it the moisture which it brought into the system. Exhausted air passes vertically downwards through the dryer. This action purges moisture from the desiccant. and regenerates the air dryer. Air is finally exhausted through the system air operated diaphragm valve (13) and to atmosphere through a silencer (14) mounted below the valve block. The pipes have a coloured band to aid identification:
Air is drawn through a filter, compressed by a piston pump, passed though a drier and is stored in a reservoir. Any air expelled from the system passes back out through the drier, taking with it the moisture which the incoming air carried. This regenerative system ensures that no water accumulates within the system, as this is a major cause of potential problems. For this reason, when working on the air suspension system, it is preferable to depressurise it using the TestBook/T4, which vents the air out through the regenerative filter, taking with it all the water. If the system is depressurised by gently cracking open the drain plug on the reservoir, the air escapes without the corresponding water, which is left in the drier. Next time the pump runs, it draws in more damp air. This can, in time, overload the drier, which will need to be changed. The choice, therefore, is either to pay to have the system depressurised with a TestBook/T4, or eventually to pay for a new drier. In the P38A the drier is mounted on the air cleaner housing. In the P38A the filter is attached to the front of the valve block on the left hand side of the engine bay. It's very easy to change. In the Classic the filter lies between the right rear inner and outer wings. Access is through a small panel on the inside of the right rear inner wing. Don't drop the filter down between the wing panels, or you're in for a fishing trip! If a subwoofer is fitted, it has to come out first to allow access - there are a large number of fairly hefty bolts to be undone. If the suspension system has a leak and needs to keep replenishing the air reservoir, moisture is continually drawn into the filter, which then becomes saturated. This will result in the accumulation of water in the bottom of the air reservoir. The reservoir is fitted under the right sill in both Classic and P38A. The Classic's pump and valve block are next to it, whilst the P38A has the pump and valve block high up on the left hand side of the engine compartment. The reservoir can be checked for water accumulation (after depressurising the system) by removing the plug and poking a finger inside. Alas, the plug diameter is small and it's set about an inch above the bottom of the reservoir, so unless you have very long, extremely thin fingers, you'll need to come up with an alternative method. As I have an objection to dropping things inside, I'd recommend siphoning with a length of plastic tube. The valve block has seven solenoid operated valves. Four corner valves each open to connect an airspring to the valve block, or close to isolate it. The inlet valve supplies air from the reservoir to the valve block, inflating the connected airsprings. The exhaust valve allows air to escape from the valve block, deflating the connected airsprings. The diaphragm (outlet) valve vents air from the reservoir to the atmosphere, via the regenerative drier. The diaphragm valve solenoid coil with the blue lead (36 ohm) is only supplied by Land Rover as part of a replacement valve block (as it has a Dunlop part number on it, I imagine there must be alternative sources) whilst the solenoid coils with black leads (4 ohm) are available separately. The "O" rings in the valves are standard sizes and can be replaced. Attached to the valve block is the (green) pressure switch, which operates the pump. Correct function of the pressure switch can be checked (after first depressurising the system) by removing the switch and inserting a pressure gauge on a "T" piece. The pump should switch on between 7.2-8.0 bar (104-116 psi) and off at 9.5-10.5 bar (138-152 psi). A pressure relief valve is also fitted to the valve block. It should take around 45 seconds to reach 10 bar, any longer and the pump's getting tired. Opening the doors or tailgate, or applying the foot brake inhibit the air suspension ECU, so the height remains fixed. Closing the doors causes the BCM (body control module) to reset the air suspension system height, which is then checked every six hours. Each time this check is made, the self-leveling resets the height to that of the lowest corner of the vehicle. Thus a leak from one corner will cause the vehicle to lose height at all corners progressively overnight. The six hour check can be prevented by removing the relay (from under the left-hand front seat base in the P38A). This will make it possible to establish if one of the corners is leaking. There are two type of height sensors. The older type have integral leads and are therefore left/right handed as well as front/rear specific. The newer type, which is the universal replacement, is interchangeable and has no integral lead. They require an extension lead which, depending on the location to which they are fitted may need to reverse the wiring. Instructions are provided with the kit. Each switch is a simple rheostat of approximately 1.3k ohms and can be checked with a simple multimeter for integrity and function. The ride height is selected by the dashboard switch (<5 ohm) and can be checked by measuring the height of the wheel arch from the ground (check the tyre pressures first!) according to the table:-
(Please let me know if you have the ride height data for the P38A rear suspension) Recalibration of the air suspension system requires a TestBook/T4 and a set of calibration blocks. Following the TestBook/T4 instructions, first the low and then the high test blocks are fitted between the body and axles. The ECU measures the output from the ride height sensors and resets the limits of the system's range. Leaks may develop in the airsprings, the plastic pipes, or at the unions between the valve block/pipes/airsprings. Leak cure is by replacement. The unions use brass sleeves to compress the plastic pipe, which may become distorted over time. The pipes are usually long enough to allow trimming and shortening of the ends, if someone hasn't been there before you, but you'll need to take off about 3/4" (1.5cm) to get clear of the old pinched part of the pipe. Land Rover supply a leak detection fluid (sophisticated washing-up liquid). Solenoid valves can be dismantled by removing the securing screws. Lift off the solenoid to reveal the valves, which can also be dismantled. The "O" rings are standard sizes, but replacements should be cleaned with dry tissue to remove any residual lubricant from their manufacture. Airpipe connections are made by collets which grip the ends of the pipes into the valve block, where there are two "O" rings. The "O" rings are standard sizes, but replacements should be cleaned with dry tissue to remove any residual lubricant from their manufacture. The outer surface of the end of the pipe should be chamfered to remove burrs.
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