P38 Air Suspension Valve Block
Failure Modes, Diagnosis, Repair
Removal & Replacement Procedure
The valve block is the most expensive component of the Range Rover air suspension system. A new one costs about $850 in the US. recently (2006) transformed the supply situation by making rebuilt ones available for about $280. As pioneering owners discovered before this happy situation came about, there are various inexpensive repairs that can be done on the valve block if it fails. The photos below show the layout of the valve block, which consists of three blocks of machined metal with air passages through them interrupted by various valves which are mounted on the top and bottom of the blocks. The system air hoses connect to the small openings in the side of the block.
Top view of valve block: the
view you would get from the center of the engine bay if you could
see through the plastic enclosure.
Valve Block Side View: left or
outer side (towards the air
Valve Block Underside View:
Valve Block on Classic Range
Rover. The whole assembly is located beside
the chassis rail next to the air tank. Note arrangement of solenoid
valves is appears identical to 4.0/4.6.
Failure Modes & Diagnosis
Leaks from Air Hose Connections:
The most common problems are simple leaks from the air hose connections. These leaks can be repaired at leisure by replacing the rubber "O" ring in the connection. After depressurizing you can press in the collet and pull out the hose from the offending connection. Then fish out the "O" rings with a crochet hook or bent wire. The "O" rings are listed in the parts catalog with the following part numbers contributed by Christian Kuhtz:
4mm lines STC2764
6mm lines (air tank and air spring lines) STC2766
8mm lines (air dryer) STC2768).
These parts do not seem to be commonly stocked by dealers in the US (they prefer you to replace the whole $800 valve block). (He also sells reconditioned valve blocks for a fraction of the new price, as well as all the other Valve Block partsis page).
In metric countries (not the US) replacement O-rings can be obtained from any hardware store. One dealer mechanic I talked to in the US has the dealer buy them for him. When Ron Beckett was getting leakage from the main airline from the tank into the valve block (a fairly common leak) he measured the "O" rings to find common replacements. He found they were 6mm I.D. and 2.5mm ring thickness. This makes sense as the air lines are 6mm OD. He used a micrometer to check the ring thickness and a 6mm drill shank to check the ID - it was a perfect fit.) He found the crochet needle as suggested in the workshop manual was perfect for removing the O-rings.
A comparison of the O-ring from Ron Beckett's rear air spring (normal O-ring) vs the leaking O-ring from the valve block. Note the valve block O-ring is "odd" in appearance on one side. The other side looks like a normal O-ring. These rings are 6mm ID and 2.5mm ring thickness.
Internal Valve Block Leaks:
It is possible for internal seals within the valve block to fail and cause strange symptoms. For example, if the seals on the individual solenoid valves for the four wheels are weak, it is possible for air to be transferred from the front to the rear springs under heavy braking. This is noticeable as a rise in the rear of the vehicle after you have stopped. Repair may be possible by replacing the individual solenoid valve seals -- if anyone has done this procedure please email me.
Other Leaks Around the Valve
Another air hose that can leak is the one connecting the valve block to the compressor -- this has failed twice on my 4.0 Range Rover. This hose is secured by threaded compression fittings (see compressor removal and replacement). Leaks could also occur from the diaphragm valve or the pressure switch if they become loose or do not have a good seal to the block.
since the valve block consists of 3 pieces of alloy bolted together, it
is possible that the bolts can loosen or the seals between the blocks
can leak, releasing air to the atmosphere. Chris Romer traced an air
leak (that was causing very slow pump-up of the suspension) to the join
between two of the blocks in the assembly (see red mark on the photo at right by Chris Romer).
Finally, although not part of the valve block, remember the air dryer is in the air circuit between the compressor and the air tank when the compressor is running, so any leak at its connections or elsewhere would release air to the atmosphere and prevent the system reaching operating pressure.
If one of the solenoid valves fails, it may be repairable using the official solenoid valve repair kit or diaphragm valve repair kit STC1803 available for about $70 (photo at left courtesy of Atlantic British). Replacement of individual solenoid valve coils is covered in the shop manual and is a simple procedure.
This is a small diaphragm operated by another solenoid. I have not had this fail (yet) but it is possible that failure of this valve could cause air to pass directly from the inlet from the compressor to the exhaust. Repair is easy using the same kit.
Pressure Switch Failure:
Failure of this unit could prevent the compressor from operating or even cause it to operate continuously (if this happens it is to be hoped the thermal cutout on the compressor would linit damage to it). Replacement is simple (it just screws into the valve block -- use plumbers teflon tape or some other sealant) and it is available as a separate part.
Pressure Relief Valve Failure:
This is the brass item that screws into the
block next to the pressure switch. Failure could prevent the system
from getting up to pressure, or (less likely) if in conjunction with
pressure switch failure could cause overpressure. A replacement one
from Rover Renovations can
just be screwed into the valve block using teflon tape or equivalent to
get a good seal.
Assembly: Removal & Replacement Procedure
I recently had occasion to remove and replace the valve block on my 4.0SE and found several items that were not clear in the official shop manual. The manual tells you to depressurize the system before messing with the valve block assembly (see depressurizing the system). In my case pressure was already low enough not to be able to pump up the suspension, so I ignored this step (do so at your own risk).
removing the compressor (see compressor
removal and replacement), the manual also suggests removing the
vacuum hose from the cruise control actuator, which I found
unnecessary. However, it is
necessary to remove the two screws holding the cruise control actuator
to the EAS control enclosure. This gives access to one of the valve
block mounting bolts -- see below. You also need to disconnect all the
air lines from
the valve block -- this is easily accomplished in a minute or two by
pushing the collets in with a screwdriver and simply pulling the air
line out (if the system is too highly pressurized, pushing the collets
in might be difficult). You can unscrew the exhaust silencer at the
lower rear of the side of the valve block, to gain easier access to the
final air line just below it. Then unplug the electrical connectors (I
usually use pliers to hold the clip open on the big one while I pull it
out) and get the wiring harness out of the way, and unscrew the three
bolts (8 mm wrench) that secure the valve block to the enclosure. After
that the valve block and the attached driver module lift easily out of
the plastic EAS control enclosure.
If you are trying to replace the driver
module, this can now be removed by unscrewing the four 4 mm Allen head
holding it on to the side of the valve block. You also need to unplug
the electrical multiplug connector underneath the valve block (C139),
which is now exposed.
If you are swapping
out the entire valve block (but not the driver module), there is one
complication. Unfortunately the
pressure switch wires bypass the valve block connector (C139) and
go directly to the underside of the control module connector C152. One
solution is to leave the
connector undisturbed, unscrew the pressure switch from the old valve
block and screw it into the new one (use teflon tape or other sealant).
The other option is to disconnect the pressure switch's two leads from
connector C152 and insert the leads from the new pressure switch into
the connector. I have performed this procedure, which is simpler than
it sounds, and is accomplished in a similar manner to removing and
replacing the solenoid leads in connector C139 -- an operation
described in detail in the shop manual under "Solenoid Coil"
replacement. The only difference is that connector C152 has a very
slightly different design, so that the miniature tabs that hold each
connector pin in place are slightly different, but they are disengaged
in the same manner. After removing the yellow cover which holds the
pins in alignment inside the male connector, you bend the tiny tab back
with a small screwdriver so the corresponding pin can be pulled out the
rear of the connector by gently pulling on the attached lead.
Christian Kuhtz kindly contributes these suggestions: "I would suggest an 8mm wrench and 8mm socket, small extension and ratchet (removal of screws on outside of EAS box, and the three silver nuts inside). Also needed is a phillips head screw driver (for removal of the cruise control mounts) and a flat screw driver to gently depress the collets to remove the airlines.
"It was helpful for me to remove the airbox lid to get better access to the harness connector at the front of the airbox. Was easiest to actually depress the clip so that the connector could be lifted up slightly and then separated."
Valve Block Repair/Rebuild
For illustrated details of disassembling, repairing and rebuilding the valve block, see the Valve Block Rebuild page.
Up until recently, Range Rover owners have had to purchase complete assemblies of EAS parts at very high prices. To remedy this situation, fellow owner He diligently tracked down the OEM suppliers of all the parts and components used in the EAS system, and offers them very inexpensively to fellow enthusiasts. All the following parts are now available from him, as are reconditioned valve blocks (about $300), driver circuit modules ($200) and much else.
The following parts are for repairing the valve block -- for details see the Valve Block Rebuild page.
Valve Block without solenoids: This has a
number (RVH100030) but does not seem to be readily available -- Land
to sell you the complete assembly.
Valve Block Assembly: ANR3901 (complete with solenoid valves, diaphragm valve, pressure switch and wiring harness).
Pressure Switch: ANR3902
Solenoid Repair Kit: STC2761
Diahragm Valve repair kit: STC1803
Air line repair kit (6 mm) STC8580
Exhaust Silencer: STC2762
Air hose from compressor to valve block: STC2760
Olive and nut for end repair of compressor hose: STC1472
O-Rings: See the valve block rebuild page for details and part numbers. Range Rover Owner
has gone to the trouble of importing complete sets of them and making them available to other owners for about $12 via his
enterprise. If you get them from him please tell him you came from RangeRovers.net!