So I was pulling a 6'x12' enclosed trailer with various loads for four out of five days. On the fifth day, on our way home, the truck got all janky w/o warning, while going down the road. Pulled into parking lot to the suspension fault warning on the dash and all four bags bottoming out! Turned truck off and then back on and went down the road a bit, only to have it happen again. Had to disconnect the trailer. This time, I used the switch to raise it to off-road height, which it did. This worked, as long as I drove slow enough and had no trailer attached. Got it home and parked it at off-road height. Next morning, no air lose. Started up and never had problem since, but haven't hooked up a trailer either! What gives??

 

Sorry to hear about your troubles. You don't happen to have a GAP tool do you?

While I haven't experienced that problem while towing, I have had several suspension faults pop up while in "normal ride height" only to have them go away when I use an electronic lift (Gap Tool). Turns out, I have a bad height sensor but I suspect you have something else going on? Sorry I'm not more help, Ill let some of the vets give their opinions.

 

Sounds like a valve body leak to me - under normal pressures they hold up, maybe with a small drop if temperatures are cold enough. Under towing conditions the pressure on the rear lines may be great enough to leak past the valve block at a high enough rate that the computer detects implausible heights, pressures, or once the air compressor enters its' "cooling down mode" you leak faster than you fill the tank and then the computer gets really pissed once tank pressure keeps dropping with all valves commanded closed.

I've had a number weird problems similar to these scenarios in my DII before I rebuilt the system to use an air tank, viair compressor, and some different valves (plus arnott springs). I can park that thing for months and it won't move a micron. My LR3 on the other hand...

Can GAP or other LR readers show you system line pressures? I know there's a few pressure sensors but I'm not sure if they're only in the tank side or what.

Can you hear when / how often the air compressor is running?

Diagnostically the height sensors should probably be ruled out if you're fine without the trailer. The only exception might be since you left it at ride height. It's fine in all heights without the trailer though? If so, then height sensors can probably be ruled out since they have no pressure on them - trailer changes nothing.

Do you know roughly what your tongue weight was? Just for my own curiosity. This would genuinely suck if I broke down while towing the horses.

 

...need to verify that there is no problem without the trailer. In particular drive it at freeway speeds and see what happens. There aren't really THAT many faults that put you at bumpstops...but one of them is a Cross-Articulation Fault, which occurs when you have a bad calibration and hit the right speed threshold (I think 60 mph).

...I went through all this $hit last summer.

 

GAP can read pressure at the gallery(?), but not individual corners or the tank. You can watch it build while the compressor runs then once it shuts off it vents the residual pressure in the gallery to presumably make start-up easier next time or prolong seal life (?)

 

Yep and that's a good way to see if your compressor is ****. If it can't make the pressure then it's either going out OR you have a leak that it can't keep up with.

 

It would have to be both though (leak AND compressor) as compressor alone would leave it on bumpstops one time and forever after lol (unless it's really weak and you went off-road to access height like 10x in a row, emptied tank, and it overheated and computers gave up and just slammed it).

Once tank has charged the springs to the new pressure for trailer tongue weight and compressor recharges tank, it shuts off like any other drive or adjustment.

The air compressor wouldn't see any pressure differences at all with a trailer. It's just charging the tank, which has a very high pressure around 300PSI IIRC. The air spring pressures on my DII range from 60-85 (loaded up, with a trailer) - those are the only numbers that would change. The springs and the seals on the spring side of the valve blocks would see the higher pressures, but that's it.

 

For God's sake man, don't suggest Rover add yet more sensors!!! 90% of my problems seem to be sensors giving erroneous readings that result in the computers freaking out, but in reality nothing is actually wrong.

(OK, it would be a cool diagnostic tool to be able to see real-time pressures in each strut - I just cringe to think of the added layer of complexity)

 

Any chance it faulted when the headlights came on only?

If it is only with the trailer connected, you might just be looking at a brake light circuit issue.

Generally if it lowers to the bumpstops(especially while driving), and will then inflate the system, you're looking at an outside source rather than an actual suspension issue.

 

As I am now having issues with no trailer attached, it is definitely a leak. I believe it is the left rear, as that is always where it starts. Going to inflate to off road and see if I can locate. Thanks all for the input!