That is not likely the issue. Neither is the leveling arms others have suggested, as those serve no function when the engine is OFF.

The telling issue is that the compressor runs with the engine off,
That NEVER happens under normal operation.
The compressors are getting voltage, when they should not be. The issue is that a relay or power feed from some (continuously hot) control module is feeding power when it should not be.

Thus not a problem with the air ride compressor assembly, nor leveling assemblies as such, but somewhere between battery and compressor assembly.

If I had to guess, sticky relay which is perpetually HOT, and that would be the cheapest fix.
But why? Never heard of this happening to anyone before. Unless it welded itself shut, due to some massive draw from a failing (or continually running compressor, meaning some other 2ndary problem). If it is the control module on the air compressor assembly, they are no longer available separately. You have to buy the entire assembly. You can find them used, but scarcely.

I recently got a lesson on the re/re of this assembly with a brand new unit, and relocation of the air intake from its utterly stupid OEM location, which was put there on purpose by the factory to ensure air ride failure. And they were successful, as most have failed.

 

I did just remember. On mine - I did have mine do the same thing about 3 times. Shut off and the compressor was running with the key out and all. On those few times I laid under the back and unplugged it by the compressor. Next morning plugged it back in and was fine. The few times mine did that were probably at least 6 months or more apart and I ultimately never did try to figure out what the cause was. Mine was a 2003 with the single compressor as well so that almost eliminates it being a compressor issue and the dual compressor uses a different software version on the control module as well so not likely software. After I reconnected mine the following mornings it acted just fine again, until many months later anyways. So I really am just not sure. If I remember right though - when at the back, if I plugged it back in right away, it would come right back on but the next morning it did not when I plugged it back in. So either a stuck relay that gets itself unstuck after some period of time, or something in the system was keeping it active and eventually timed out. Never did have an error message when it happened either.

 

Good info MixmanSC. So now I DO know of someone else this happened to. You.

Hopefully he can narrow it down! I am curious how this turns out.

For the OP, unplug the compressor, or you will burn it out. That is how leaky air bags burn them out.

 

Quick update. I pulled the AS Electronically Controlled Air Suspension Relay. Did a quick check of continuity across Pins 87 and 30, found it shorted. Rapped it. Tapped it. Shook it. Still came up shorted. New relay is arriving today. I'll post again the operating status of the entire system once I install the new relay. I am fearful, as finall suggested, that there is something else going on that first caused the compressors to run continuously, and which, then caused the relay to fail ("weld shut"). The only DTC thrown was the C0711 (which I detailed above). After clearing the codes and then pulling the relay, the only code that came up was C0712 which was expected because there is no power to the AS without a relay.

Just curious fianll, what is it about the location of the air intake that causes early failure of the AS system? If I recall correctly, it's placed up next to the fuel filler neck (almost exactly the same as the rear diff vent line on my TJ). My guess is that this was the highest and cheapest (easiest) location to engineer and design and I'm wondering what conditions exist at this location that makes the system fail.

 

Well, this is the 3rd time I've tried to post a reply to my own thread. Seems the previous 2 are flying around somewhere in the Ether-world.
Regardless, I replaced the relay to the Compressors, everything now runs fine. No codes, no leaks, everything looks good.
I intend to carefully cut the side off the old relay to see if I can see where the main contacts may have been stuck.
Thanks everyone for all of your advice, suggestions, comments, etc.

 

Well, now I'm wondering where those two other posts went???
For now, I want MixManSC to know that he was absolutely correct on the location of the relay, it is indeed on the firewall pinned to a small angle bracket just about a foot below the master cylinder. Mine was so grimy that I could hardly see it. Once disconnected from the bracket, it does stick out towards the left front tire just like in the pic posted by MixManSC. Plus, a question for finall: Do you have any additional information related to the location of the air intake and why that location specifically causes problems with the AS system? I know the intake and filter is tucked up behind the gas fill neck. I'm curious why this would cause a problem with the AS. Also, for Oceanbrave, I did check G402 as well as G405, both were in great shape; also, if I find a PN 88982408, I'll let you know. Seems most parts I search for are no longer available and that's bad news for somebody that owns two H2s!
Thanks again to everyone.

 

The air pickup and filter is located right behind the RL tire, and is near the bottom back of the inner wheel well. As such, splatter from the RL tire which is not caught by the inner wheel well shoots directly into the filter. The filter is just a fibre puck. And lets the muddy water which it is coated in, to suck right into the solenoids. That causes the failure.

What everyone reading this post should immediately do, is to lengthen the black ~3/8" polyurethane tubing (available from SMC) and extend the filter up the gas filler neck, right up behind the gas cap. You can access that area by removal of the gas filler bucket, and strapping the filter/tubing as high up on the gas filler neck as possible. You can also re-bend the stiff OEM tubing with a heat gun, but be very careful, as it turns from solid to liquid in a narrow temperature range. You will still need to lengthen it. You can buy a coupler from anywhere that sells tubing, or make your own.

Of course wash out the filter first. That can be done by *Carefully* sliding back the rubber sleeve from the plastic filter (with help of lube), opening the filter, washing said filter, drying, Or buy a new one for $150.

This will avoid future failures due to the air compressors full of muddy water.

 

Thanks finall! I did take the AS power supply relay apart. I didn't have to cut it open, I just tapped the little black spot on the back with a 1/8" punch and the entire relay fell right out. I did find that the contact for the power to the compressors (between Pin 87 and 30) was burnt slightly and had a small bit of build up of crusty burnt stuff on it. It wasn't much, probably just enough to make it stick. Also, this afternoon when I checked it (before popping the guts out), the relay was open which was contrary to what I found when I first took it out of the truck a couple days ago (I posted about that, but, well, post disappeared. because science I guess). I think that overnight, when temps dropped to under 20, the metal contracted enough to break free the contact point. Anyways, all's good. I'm off to clean the air filter and lengthen the tubing to it. (I am holding my breath a bit yet, not quite convinced that all is really well - something other than age (93K miles) made that relay stick shut).

 

Good to hear it was just the relay! Over many years the contacts just get worn some but I think it is often more that the spring and coil are wearing out that causes them to eventually start sticking. If the action is too slow that current has more time to arc and start to weld the contacts together.

 

Thank you MixManSC for the heads-up on the filter, I'll put that job on the todo list.

PA05H2 seems like positive news 🤞 your theory about the temperature sounds plausible.

For my AS troubles it turned out to be the ECU, ended-up buying a 2nd-hand unit which was cheaper than a new module on it's own, currently restoring my old one as a back-up.hence my interest in all parts AS related.