Thursday, June 2, 2011

XJ – Vehicle Dynamic Suspension

Remember the good old days where front end repair were considered easy tickets? All you had to do to know if a spring was good or bad was measure the ride height. Shocks were easy to change, and springs had a lifespan longer than 3 years… If you don’t know what I’m talking about after this article you will. Here is how the new XJ’s Vehicle Dynamic suspension works, some troubleshooting tips and experiences to add to your diagnostic repertoire.

First of all, what does this VDS (Vehicle Dynamic Suspension) do? Besides improved, softer ride comfort the VDS provides vehicle leveling regardless of load. When the vehicle is moving at fast speeds, this system will actually lower the vehicle ride height to improve aerodynamics, then return the vehicle to normal when the speed decreases. Neat huh? The VDS also makes sure that the vehicle is at the correct hight for the varying load conditions: more passengers, the wife’s shopping bags, the dead bodies in the trunk…In other words, its job is to keep the vehicle at desired height no matter what you do.

The VDS performs its functions by a valve body which either directs or exhausts air to and from the air springs. The air is supplied by a reservoir, and if no air is available in the reservoir, a compressor. The ASM (Air Suspension Module) controls the operation of the valves in the valve and that’s how it’s in charge. It also controls the operation of the compressor. The front air springs are operated together, and the rear are operated independently of each other. It is also important to know that when lowering the suspension the front is lowered first, and when raising the suspension the rear is raised first. The reason is simple, to avoid headlamp glare. For example, if the rear was to lower first then the headlights would aim upwards and could blind another driver.

The VDS system features two different speeds for adjusting the suspension: fast and slow. The fast speed takes place when the vehicle is stationary and you load the vehicle with weight, for example, load your gyms dumbbells on your trunk. The VDS will adjust the rear suspension with the fast filter. The slow speed takes place while driving. There are little changes in weight when the vehicle is moving, for example, fuel consumption makes the rear of the vehicle eventually lighter, these changes are adjusted with the slow filter.
The most common problem with these systems is (you guessed it) air leaks. By experience I can tell you that those springs will leak. The springs are included with the shock as a strut assembly. Their lifespan (by personal experience) is from 3 to 6 years. I haven’t replaced one single compressor or reservoir yet. If you want to know which one is leaking (sometimes is hard because the module adjusts all of them when one is leaking) just remove the VDS fuse. That way the car can’t adjust and the one lowered will be the one at fault.

The VDS system has different modes of operation that can be usually changed with the factory scan tool or a very good aftermarket tool, like Autologic. Here are the modes of operation and how they operate:
  • Transportation mode: the car arrives at the dealer in transportation mode and they will have to change it to customer mode before selling it to you. In this mode the vehicle sits high up for loading and unloading of the vehicle.
  • Customer mode: all the modes except transportation mode are enabled in this mode.
  • Sleep mode: after you leave the vehicle at night it goes into sleep mode after 30 minutes. In this mode the car wakes up every 24 hours to check the height and it will lower it if it's incorrect. It will never try lift the vehicle though.
  • Preliminary mode: when a door or the trunk is opened, or the engine is shut off from a standstill condition, the car goes into preliminary mode. In this mode, the reservoir keeps the vehicle from within greater tolerance than in stance and drive mode.
  • Stance mode: when the engine is running but the vehicle is standing still, stance mode will adjust the vehicle height to correct values. 
  • Drive mode: when the vehicle speed is above a set value, the compressor is used to lift the car, the reservoir gets replenished, and all of the VDS functions are enabled, such as height lowering at high speeds.
For a list of trouble codes and their possible causes:  Vehicle Dynamic Suspension DTCs

The automotive industry has change much over the past years, and nothing says it won’t continue to do so. Suspension systems went from a simple spring and shock to an air spring with integrated shock, and a control module with a compressor… you get the picture. Having a basic understanding of these complicated systems will make you a better mechanic, owner, and enthusiast.

Another link of interest might be about the removal and installation of the front Air shocks. Here is the link: http://www.jaghelp.com/2015/01/how-to-change-front-air-springs.html

37 comments:

  1. Good article and it helped adding some new information which I needed. It almost seems like when you are moving your car, it automatically acts to control your handling for a perfect control over your car.

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  2. Every car part is important. Especially if you can really feel the difference when you test it after installing it. There are a lot of proven and tested car parts out there that are so much reliable to use.

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  3. If a road were perfectly flat, with no irregularities, suspensions wouldn't be necessary. But roads are far from flat. Even freshly paved highways have subtle imperfections that can interact with the wheels­ of a car.

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  4. It's great. I really must have the VDS (Vehicle Dynamic Suspension) with my car.

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    Replies
    1. oh yeah, but once something goes a miss, you will be praying for the old cheaper simpler spring system

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  5. can the vehicle reset itself to transportation mode after the suspension has been replaced, and if so how can it be reset to customer mode ?does anyone know?

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    1. I've seen it before, don't know exactly how or why though. In those cars you need the factory scan tool to reset it to normal mode, or some very good aftermarket. We used Autologic.

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  6. I just replaced the front air suspension on my Jaguar xj8, and now it looks like I went from a low rider to a 4 wheel drive! this is becoming so frustrating and costly, if anyone has any information that could be of help I would greatly appreciate it.

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  7. Just replaced the rear air dampers, relay, and compressor on my XJ8 2004. My rear is still lowrider, the system is not raising vehicle at all, any help

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    Replies
    1. Frank, you throwing money at your Jag and hoping something sticks seems quite foolish. Throw your money at someone with a factory scan tool and some knowledge of Jags. You will better off and enjoy the true capabilites of the CATs system

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    2. I agree. But since he went all this trouble, have you tried disconnecting the battery over night?

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    3. These cars also have a level sensor. Its possible that has malfunctioned as well. Id also check the distribution block located under the spare. They are known for getting a little rusty inside(even though it looks new outside)and causing a sticking issue with the solenoids. And keep in mind that like I mentioned above if you don't go and see a professional with the proper scanner tool he cant set the height values....therefore your car will be a low rider. Spend the cash with true diagnostics because these cars aren't Yugos and deserve the best....and not for nothing I would NOT disconnect the battery over night it is absolutely false if you believe that doing so resets anything. Good luck

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    4. I miss the good old days where cars were simpler...

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  8. Would love to see someone follow up with there problems just once. It can only help other owners with similar problems if it was repaired and working. Nothing like reading peoples pleas for help on forums all the time and than...NADA. oh well

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    Replies
    1. agreed that's why i started the blog as a jag specialist i get to see the problems more than once. my set back is that i can't stop and take pics too much while at work!

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  9. I had problems with the air suspension and installed the Arnott conversion kit. Everything works fine except that the "Air Suspension Fault" message will not go out. Supposedly something changed in the 2008 XJ from prior years and so no one can figure out how to shut off this message.
    Strutmasters said that they provide instructions on how to unplug a black box module located behind the back seat. This would eliminate the "Air Suspension Fault" light but would cause the "Check Air Suspension" light to come on. This light could be shut off by selecting "reset", but it would have to be done each time the car is started.
    Any ideas? Thanks

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  10. To enter my garage, I need to raise the car ¼ inch. Can the suspension be modified
    for manual control?

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    Replies
    1. No, but you can bend the height sensors a bit to trick the suspension and raise the car 1/2 an inch... although I don't condone this...

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  11. Nice information! I am intimidated by the excellence of information. There are a lot of high-quality funds here. I am sure I will visit this site again soon.
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  12. thanks for that article, great advices for new users. i’m following most of the mentioned tipps thanks

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  13. I have a 2004 Jaguar xj8 and,my air suspension fault light is coming on. just today the light came on and just the driver side back suspension appears to be raised super high and the rest seem to be normal. also new was that the engine light came on. I remember having a problem with the air suspension fault light coming on several months ago with heavy rains and again last night we had heavy rains but I don't remember my car being jacked up on one side and riding hard... any ideas or suggestions --- Signed, frustrated

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    1. This is precisely the problem I have encountered with my 2006 Vandenplas and definitely began after heavy rain. Scans and resetting of codes have not solved the issue. Would be interested to hear if and how you resolved your malfunction.

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    2. Water engress is damaging the module for the rear shocks.. you have water inside the module connector, needs disconnect clean water and re connect module under rear seat. Stop water from getting in car

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  15. Hi. I have 46K miles on my 2004 X350 and had "Air Suspension Fault" light to come on. Before going through expensive and most times unnecessary replacement of shocks, check out the compressor. If it's running and the car is not raising, very common cause is worn out (PTFE) piston ring. Requires rather simple 1/2 hour disassembly an reassembly. Instructions and $23 replacement kits available online. Good Luck!
    http://www.ebay.com/itm/WABCO-AIR-SUSPENSION-COMPRESSOR-PISTON-RING-REPAIR-FIX-KIT-/151062196353
    https://www.youtube.com/watch?v=_BwGaP4Zaqc

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  16. Help! Got a 2004 Jaguar XJ8 with 95,000. For several months the "air suspension fault" with come on very erratically, sometime 2-3 times a week, sometimes not for 2-3 months. Jaguar code, C2303 comes up with tested by Jaguar. Have checked suspension heights on all four wheels, and LF, LR and RR all appear within specs. However, RF is about 1" down from the LF. C2303 code says compressor failed, yet only the RF appears to be out of whack. Everything I read says only the rear suspension operates independent of each other. Would this indicate the need for a new RF air suspension strut, or a problem with the compressor

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  17. Sounds like one of the front air springs is failing. I had one go bad in an unusual way. the compressor was running longer than normal so I jacked the front of the car and after 6-7 inches I started to hear an air leak. the passenger spring would hold air at lower heights and lose air at higher heights. The other times I had failures they just blew out catastrophically. (had the two fronts fail within minutes of each other) Replaced the faulty spring and back to normal.

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  18. We have an 2008 XJ8 in our shop with failed right front air spring leaking. We replaced air spring and cleared codes with autologic scan tool. The Air Compressor was working during testing, but does not engage now. We tested the #1 relay according to Air suspension schematics and other articles read. No. 6 fuse is good, and no faults return. Still no air compressor and no fault codes returned. We feel the system should turn on the compressor but does not. Please advise of what we may have missed.

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  19. Keep posting the good work. Some really helpful information in there. Bookmarked. Nice to see your site.current speed

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  20. which company sells the parts needed for the compressor, Sensor, springs etc. How much should I expect to spend to replace these things?

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  21. I have a 2004 XJ8 that had a leaky trunk and got water in the wheel bed causing some wire issues. Those were fixed, but now the suspension is acting up a bit (no engine lights on though). I sucked it up and paid the diagnostics at the dealership even though they always rip you off. They are saying I need a new CONTROL MODULE - JAGUAR (C2C37299). I have two questions.

    1) - can I buy this part after market (how much labor intensive is it) - Jaguar wants $1250 to fix it.
    2) - will I damage the car if I don't fix it. it's not jacked up on one side vs. the other, just slightly lower than normal @ all times.

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  22. I am looking to purchase a 2008 XJ with 35,000 miles from a Jaguar Dealership. I was sent some pictures last week and new pictures today. The pictures today show the front end sitting very low. The very top of the tire is at, maybe slightly in, the wheel well. On the prior photos,the car appears level at all for tires. Why would the occur?

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  23. hope you did not buy that car or at least had it check out and not by that dealership

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  24. read these articles with interest I own a 2007 xj lwb diesel having problem with car suspect suspension. ive got a ripple type vibration when going over any imperfection on the rd.ive had new compressor fitted.
    new lower wishbones with poly bushes fitted. New anti roll bar bushes fitted. rear gearbox mounting replaced, and today I've had the car properly aligned. Would you suspect the air bags after all this work. I'm prepared to replace them but worried I could spend all that money and still have the problem. Would it be the valves as suggested above that would cause this. the car has done 284,000 miles.
    thanks BB.

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