So, long time no post, but I've run into something I could use a little help with, and yep, it's the wonderful air suspension! So, what happened: I was driving home from work on Wednesday when about 5 min into my drive the AIR SUSPENSION FAULT popped up on the dash and the car felt like every bump was a kick in the pants. Got home and noticed the drivers rear wheel was basically to the ground, lower that even a deflated shock should be. As I have seen this before (replaced the fronts just last year) I figured bad shock, after all, they are original on the rear and have over 200,000 miles on them. Ordered up a RMT unit, just got here and installed it. Drove around a bit for the car to adjust itself and guess what, now the whole back end is on the ground and AIR SUSPENSION FAULT is back. Here is what I have tried:

1) As mentioned, new shock. (Didn't fix it)
2) Disconnected battery and touched +/- cables incase the system was just messed up (No fix)
3) Checked all the height sensor/air connections (All good)

Now, here is what I have noticed: First - I just went out to the car and when I opened the door, I could hear the tell-tale noise of a working reservoir opening and a little air coming out to try and fill the shocks (hard to describe but all of you will know what I mean!). So it seems the car knows the back end is low and trying to add air, but the reservoir must be empty. Second - in the past whenever I did suspension work and the car would be on the ground when I finished, after running it for a few min it would immediately regain it's normal height. Sometimes I had to drive a little bit but it always came right up and I could always hear the compressor running.

So, taking this into consideration, it seem the situation is the following:

The car knows it's low and can't fill it back up. The shocks are good, the height sensors are good, the reservoir, valve block etc are good. The compressor may not be running. In regards to the compressor maybe not running, I have checked the fuses (all good), the relay might be bad? I think I have a spare to swap in and see what happens (I know relays can just kinda go bad). That leaves the compressor failing possibly.

Solutions? I'm thinking the following course of action:

1) Swap the relay as I mentioned
2) Take the splash guard out and see if the compressor is working (give it direct power if I have to)
3) Based on 1/2 results, rebuild compressor.

Now this system was working flawlessly until Wednesday. I find it hard to believe a compressor would just go. I'm thinking electrical issue (relay or the like). The easy thing would be to hook up my VCM and use IDS 118.5 to scan the car and let it tell me what is wrong. Problem is, I tried that and IDS wouldn't load my VIN info at the first stage when it says enter las 6 of VIN (working fine on my wifes STR), it just goes to a blank screen. I did a uninstall/reinstall a few times and now the whole program won't start (getting tabman and testman errors even though the programs are there and not blocked by the firewall).

It's been a long day, it's dinner time, and I need to take a break so I'll try the relay swap later (as long as I can find the spare I have). Just seeing if anyone has any better ideas on how to approach this or have I covered my bases?

Thanks

PS. Just to add there is NO vehicle too low warning.

 

Has the compressor been replaced ? These don't last forever, and at some point fail to charge the compressor within a fixed value of time. This throws up a fault code and message. At the same time CATS defaults the shocks to "Hard". So you need to get the codes read.

Other thing to think about is - could one of the rear suspension height sensors be defective. Again these don't last forever.

However with no fault codes to guide the investigation, you are in the dark. Best not to spend any more money until the fault codes are read.

 

Thanks for the quick reply Fraser,

Ya, my thinking is inline with yours. I'm still trying to get my IDS to work, it was working, reinstalled it, and now its not. I've had this VCM and IDS for a few years now, worked perfect on the STR and when I really need it on the XJ, it craps out! Who knows what's going on, still working on that.

I find it odd though that I don't hear the compressor running like I normally do. I know it was replaced at some point, but it could have been 10 years ago for all I know. I'm not throwing any more money at this, that's for sure. I don't feel bad about the new shock since I was thinking about doing those anyway since they are original, and now I have a spare if the other one blows, but that was only about $230. If the relay swap doesn't work and I directly power the compressor and it works fine, I'm not replacing anything until I get my IDS working to properly diagnose it. I know without codes it just like taking shots in the dark. Again, since I hear the tell-tale sounds of a reservoir and ASM trying to add air, and I did hear some air being let out of the front to level it (it was a little high) I'm thinking something simple (sensor/relay etc). Enough speculation for now, it's the weekend and I'll have some time to work on it tomorrow to see what I can do!

 

Hi WinterJag,

Just a couple of initial thoughts:

1. Have you actually driven the car, or only run the engine waiting for the suspension to repressurize? If the ASM has entered Jacking Mode, it won't re-enable suspension operation until the it detects that the vehicle is traveling over 2 mph.

2. Several times I have experienced that when the Air Suspension Fault is triggered, the ASM will not resume suspension operation until the codes causing the ASF are cleared. I hope you can get your IDS back up and running. Have you remembered to disable your anti-virus and firewall? Does your version of IDS require the date of your computer be set back in time?

Cheers,

Don

 

Thanks for the advice Don, but I have done all that! I did drive it around a few times after I let the car back down and same issue. But some good news, I got my IDS up and running! So, I just scanned the car and cleared all the million fault codes everywhere (first time ever on this car) so I'm starting from a clean slate. I did have the leveling plausibility error code in the ASM, but that could have been from when my front shocks blew out. But since I cleared them, I can start from scratch. Now, I did manage to check the rear height sensors and they are working. They know the car is low (reading around -27mm) so they are working. That basically leaves the compressor. I replaced the relay with a known working one from my spare engine fuse box, so that should fix that if it was the problem. The one thing I can't figure out how to do in IDS is manually tell the compressor to turn on. Something interesting happened while fiddling around with things. I was telling the car to inflate the rear suspension, nothing happened (but I did hear the valve block in the trunk trying to open and add air). I told it again, nothing. Then I told it to inflate the reservoir, nothing, tried again, and I felt and heard the compressor fire up for a bit. Tried the leveling again, nothing, reservoir again nothing. So it seems to point to the compressor. BUT, I know you can tell it to turn on in IDS (at least I think you can!), and that would be the definitive test if it doesn't turn on. Anyone know how to do this? I'm pretty good with IDS, but never had to dive in this deep before and when you get this into it, I'm not a fan of push buttons and see what happens!

Just to add, I did take the car for a drive around and still no luck. The interesting thing is that now there is no AIR SUSPENSION FAULT light coming up either. So, it almost seems like even though the height sensors know the car is low, it's just not trying to raise it up, or can't raise it up. I would think the latter would trigger the error light.

 

With no compressor (and presumably no air in the reservoir) shouldn't the front start dropping after awhile? I would think that if the front is staying up you have pressure (so the compressor does not need to run) and there is an issue with the valving (stuck shut) or pressure lines (blocked) to the rear shocks.

 

Sir, with you especially being located in the colder northern latitudes, my best and only advice to you is to switch that vehicle over to Arnott coil/springs. This is what I had done to my 2005 Jaguar XJ8L shortly after I purchased the car in 2014, and I have never looked back. In many ways, the ride and handling with the Arnott coil/springs is actually superior to the former air suspension system.

 

Well a little update. First, Rickkk, I actually just moved to the US for work, so I'm in PA now! Second, no way I'm going to Arnott, just not going to happen. I like the air ride and with 4 known good shocks and a spare, why change. Pragmatic, my thoughts are your thoughts. The front stays up so it has to have pressure.

Now the new info. I needed to get gas so I decided to take it to see if it would just need a drive to air up. Before I left, I decided to just jump the compressor at the relay and guess what, works perfect! So the compressor is good. I then went to get gas and a bit of a drive, the fault came back. I stopped, turned the car off and on again, fault goes away, but then came back seconds later. This says the compressor isn't running and tripping the fault since that take about 2 min. Also, the rear left came up a bit but the rear right is still slammed, maybe slightly higher, but still down. Got it home and scanned it, only code in the ASM C2302 - Leveling Plausibility Error. Ok, next I monitored all the rear height sensors and reservoir pressure. Got the following numbers:

Pressure sensor: 4.5bar
Rear passenger height sensor - +22mm
Rear driver height sensor - -15mm
All the voltages were correct at the sensors, reservoir etc.

So, this looks to me like the system is perfectly pressurized and that is why the compressor isn't kicking in. It seems that the car thinks the rear passanger is high (when it's actually low) and therefore is trying to level but can't release any more air out of the drivers side to match the passanger. And the solenoid noise I hear in the trunk is actually the system trying to RELEASE air, not ADD air, but since the shock in fully deflated, it can't and flags the AIR SUSPENSION FAULT.

I do remember going over a BIG pothole a week or two ago on the passanger side. Maybe it knocked the height sensor ajar and threw everything out of whack. I'll have a look at it this weekend and see what's what and if all else fails, I'll just tighten up all the height sensor bolts and then re-calibrate the ride height since my IDS is working. Hopefully that'll do it! I'll try to get on it this weekend as long as real life things don't get in the way.

 

I don't remember if SDD (or IDS) has a direct command to run the compressor, but it does offer the options to inflate the front or rear suspensions. You could try starting a diagnostic session by selecting a problem with the compressor to see if the recommended candidates or actions includes a compressor test.

At this point the most expedient solution might be to try recalibrating the suspension. You will need to enter the distance from the wheel centers to the lip of the wheel arch in millimeters, so you'll either need a metric rule or tape or to convert to mm from inches. I have found that often in the calibration procedure the initial result is less than perfect, so you have to run it again and "lie" to the system to tell it a wheel is a little lower or higher than it actually is to get SDD/IDS to overcompensate so the result is where you want it. The factory ride height measurements are listed in my summary of the air suspension:

Air Suspension & ECATS System Summary: Components & Operation

Cheers,

Don

 

Have you ruled out the RMT strut isn't leaking badly? One of my RMT struts has a noticeable leak. It will hold enough air to drive around, but if I leave it parked for more than a few hours it will drop and I will get the "low" warning.

 

A friend of mine had a defective strut from RMT, they recently had a batch of bad bladders that rupture prematurely. We chased down every single item on his air suspension, it was the strut the whole time.

If your car lays out overnight its 90% the air strut CALL RMT AND GET A WARRANTY REPLACEMENT

 

Thanks for the advice, but it it NOT the new strut. The issue is the same with the old and new RMT strut. I did think of that, but also ruled it out by swapping the old one back in. Based on the height sensor data (gave it another check last night) I can clarify I swapped the sides in the post above by mistake. Basically, the car thinks the rear drivers side is high (+22mm) and the car is trying to lower it (I hear the valve block trying to vent air), but since it is already bottomed out, it can't be lowered, hence the leveling plausibility error triggering the AIR SUSPENSION FAULT. The air suspension is functioning properly, it is just getting faulty values from one sensor. A recalibration should do it, just haven't had the time. I hope I can get it done tonight or tomorrow. But since I can just drive the wife's STR, I'm still in a Jag, so can't really complain and have less of an incentive to get it done!

 

Take a look at the height sensor and attachment. Then jack the low side up and see how it changes. If it still reads +22 either controller or mounting is broken.
RMT rebuilt an Air spring for my A8. They forgot to bleed off the test pressure. It was too long to install. Once installed at top, I had to jack up car to get the system to bleed off air pressure. Then I could connect to the LCA.

 

Good advice Panelhead. I still haven't got to this yet (stupid real life and work!), but I like that idea. I will jack up the low side and check the height sensor reading. I know the mounting is good since I had a good look at everything when I had it apart, but as you mention, it's possible even though the voltage is good maybe the signal/controller isn't. I'll have to check that out. My plan now is if I jack it up and it all looks good on the sensor, I'll just recalibrate it and see if that does it.

Regards to RMT springs, I've got three of them now, and seem to be holding up ok with no install issues as you had. Now, I did have one of their shocks blow out on me right after installing it with the fronts, but there was an obvious assembly error and they sent me out a new one super quick. In the end, the stood behind their product and their replacement was from a new batch since apparently there were some issues with a few shocks of theirs.

 

Well, big thanks to Panelhead for the advice on watching the sensor reading and jacking the low side. That is exactly what I decided to do. First, I fully deflated the system, checked the readings, and all but the rear left was reading as expected (-80mm or there about). Then I reinflated and the readings changed upfront, but the rear didn't inflate (since it thinks it's high). Checked the readings again and the front was basically perfect (+1mm), rear right said -83mm (good reading since it slammed to the ground) and the rear left said +27mm (clearly wrong). I then grabbed the jack and lifted up the rear left side about 1 inch. Checked the readings again. Well, guess what, rear left still said +27mm. The rear right and front realized the car height was changing as they moved by a few mm, they are working fine. So, looks like I need a new height sensor!

 

Just thought I'd wrap this up. I finally installed my new height sensor and all is well! I ran the calibration after it was installed and other than a little fine tuning (front right is about .5 inch higher that left front) it's good to go. Finally, a problem that was a simple (relatively) fix!

 

All,
I may have a similar issue with my girlfriends '04 XJ8. I'm new to XJ8's,I have a '87 XJS but this is a very different car. She thinks she needs one rear air shock replaced. Apparently she had the other three replaced last year at some point. Any thing special I should look for or stay away from. Any particular brand to look for or stay away from. She is on a budget and I am not assuming her Jaguar repair bills. I have access to a lift so I can do the work myself. Thanks in advance.

 

Hi BradsCat,

My first question is why three of the air spring/damper units were replaced and not the fourth. What were the symptoms then that prompted the replacement? What are the symptoms now that are leading her to conclude she needs the fourth unit replaced?

For a basic primer on the air suspension, see this link:

https://www.jaguarforums.com/forum/x...2/#post1597274

Cheers,

Don