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Discussion Starter #1
Hi everyone, new member and I've scoured the forums for this issue I'm having. One of many but I love the truck regardless :) my new 08 QX56 has the air suspension and more often than not it's fully inflated and jacked up. I haven't towed or put any load in it yet other than a couple groceries. Every few rides I'll park it and notice it's leveled back out with the front but most of the time the back end is 2-3" higher than it should be. Rear end sure looks mean like that but it ain't right.

All the mentions in the posts are failing, sagging suspensions. Mine has never gone low the few weeks I've had it, only back to regular ride height, level with front. I've got the opposite issue.

I've already mortgaged this with the dealer getting the safety items done. What am I looking at replacing? Is the first culprit the ride height sensor or is there a relay that sticks? I don't hear the compressor running all the time or anything. If I swap out the ride height sensor with a need one.. can I just swap the part or do I have to go to dealer to recalibrate/null out the ride system?

Thanks!
 

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Discussion Starter #2
Anyone have any ideas here? I noticed it seemed to do it more with the winter weather mix but we've also had dry roads for the past two weeks here and it just started doing it again this weekend. Could the relays be sticking or is this the height sensor acting up?
 

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There is a release valve built into the compressor that allows the shocks to air down when ride height sensor dictates. Sounds like you may have to adjust the ride height linkage. The linkage is located on the driver side lower link next to the lower coil spring seat. If after adjusting the height does not decrease I would suspect the release valve is not working.
 

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Discussion Starter #4
Thanks. Yeah I've looked at the height sensor. Trying to figure out if I bite the bullet and just replace it first, or if there's something else to try. If the release valve is bad does the whole compressor have to be replaced?
 

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Thanks. Yeah I've looked at the height sensor. Trying to figure out if I bite the bullet and just replace it first, or if there's something else to try. If the release valve is bad does the whole compressor have to be replaced?
Yes, the valve is part of the compressor.
 

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Discussion Starter #6
I'll try tinkering with the ride height sensor and see if that helps. When it works it seems fine and level though. Maybe it goes haywire and over pumps the system for a bit ? if that doesn't help I'll manually 12v the connector on the weekend and see. Appreciate the help ?
 

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Discussion Starter #7
Oh one more Q.. if I replace the ride height sensor do I have to get the dealership to zero/reset the system or is it plug and play? Thanks
 

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It is plug and play. No reset needed.
 

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Have you checked the 'height sensor', item #3 . That is the sensor that detects the height. It might be loose on your end, and not noticing that it needs to lower the truck. Once you turn the truck on, within 20 seconds it is supposed to activate (ON) the compressor to raise it, I think to release it is 2 minutes. I had to deal with my compressor and a strut that were leaking last year.
 

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Discussion Starter #11
Hey thanks for the diagrams! I haven't tried adjusting the sensor yet but it was tight where bolted. I'm going to try cycling the release valve by loosening and turning it to fake it being too high. I guess that would tell me that either the sensor is bad and/or the relief exhaust valve on the compressor isn't working. I'd take it to the dealer but already racked up a few grand with them fixing other things on it this year
 

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Hey thanks for the diagrams! I haven't tried adjusting the sensor yet but it was tight where bolted. I'm going to try cycling the release valve by loosening and turning it to fake it being too high. I guess that would tell me that either the sensor is bad and/or the relief exhaust valve on the compressor isn't working. I'd take it to the dealer but already racked up a few grand with them fixing other things on it this year
Try removing the ball-joint with a small flathead and move it down, wait 2 minutes, and it should start releasing air at the compressor side. If that doesn't work, I guess try shutting the truck off, wait 10-15 seconds, move it up, and at 30 seconds the compressor should start pumping. If that is happening, that means the sensor is sending out the signal to pump, so the switch is good, but it seems like your release portion of your compressor is not. You know you could empty the bags by hand by releasing at the compressor one of the 2 lines. Press the ring in with fingers, and the pull the hose with the other hand, it will open the system and release all the pressure. After that, I would suggest to put the ball-joint back on the system, and turn the truck on, 30 seconds, it should start pumping. If it pumps too much again, then the sensor is still working, just too high. Maybe you have pumped too much air in the past, and the release portion of the compressor is not working. At that point, I think you have to replace the complete compressor; I had to, but mine was leaking at the back side. I got it from Amazon for $261; I see it now for $279

https://www.amazon.com/gp/product/B00U0AAF14/ref=od_aui_detailpages00?ie=UTF8&psc=1

Let us know what's up!

Good luck
 

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Discussion Starter #13
Awesome thanks for the insight. I'm going to tackle this Friday or Saturday and will follow up. I did find the height sensor for about 90 and Sun core makes a compressor unit and it's on sale for about 145 which seems great. Only thing it has 4 outlets but I'm guessing that's universal and you just hook up 2. Is it safe to just pull a line out like that or is it under pressure? Ron.
 

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Awesome thanks for the insight. I'm going to tackle this Friday or Saturday and will follow up. I did find the height sensor for about 90 and Sun core makes a compressor unit and it's on sale for about 145 which seems great. Only thing it has 4 outlets but I'm guessing that's universal and you just hook up 2. Is it safe to just pull a line out like that or is it under pressure? Ron.
Yes, you may pull the line; simply push the red ring in, may have to use a small flat-head, as I had to the first couple of time just to loosen it up, and you pull the line out. Pressure will come out and both sides will lower. At that time, watch how the sensor reacts and moves, what movement would turn it on and what would turn it off. Unhinge it, and do it manually to the fill position. Turn your truck on, 30 seconds, the compressor should start filling, after 15 seconds or so, I would move the sensor to the other position, and it should stop. If it stops, well, your sensor is good. At that point I would move the sensor the other position all the way so the sensor sends the signal to release air, I believe it was 2 minutes, at all this time the truck stays on. If after 2 minutes the compressor is not releasing, I would have to point towards the controller on the compressor itself, what receives the signal to release air.

PERSONALLY, I replaced my compressor with an OEM one. Yes, it's $270 instead of $145, but you get what you pay for I guess, and if you are keeping the truck for a while, might as well make the investment. Just like when I replaced my leaking left-strut at the connector, I did OEM, sure, $112 vs $80, but rather have the original Nissan part in there. You are already saving a lot of money by doing it yourself and asking here, might as well spend the money on the part; at least that's who I see it everytime I get help from the forums. :)
 

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Discussion Starter #15
Yes, you may pull the line; simply push the red ring in, may have to use a small flat-head, as I had to the first couple of time just to loosen it up, and you pull the line out. Pressure will come out and both sides will lower. At that time, watch how the sensor reacts and moves, what movement would turn it on and what would turn it off. Unhinge it, and do it manually to the fill position. Turn your truck on, 30 seconds, the compressor should start filling, after 15 seconds or so, I would move the sensor to the other position, and it should stop. If it stops, well, your sensor is good. At that point I would move the sensor the other position all the way so the sensor sends the signal to release air, I believe it was 2 minutes, at all this time the truck stays on. If after 2 minutes the compressor is not releasing, I would have to point towards the controller on the compressor itself, what receives the signal to release air.

PERSONALLY, I replaced my compressor with an OEM one. Yes, it's $270 instead of $145, but you get what you pay for I guess, and if you are keeping the truck for a while, might as well make the investment. Just like when I replaced my leaking left-strut at the connector, I did OEM, sure, $112 vs $80, but rather have the original Nissan part in there. You are already saving a lot of money by doing it yourself and asking here, might as well spend the money on the part; at least that's who I see it everytime I get help from the forums. :)
Thanks Alex, totally agree :) You guys are awesome, appreciate all the help. I'm going to do this tomorrow or Saturday and will post back. May help some others in the future too.

Ron
 

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Discussion Starter #16 (Edited)
So.. Tested it all out. Everything works when truck running if I manually adjust the height sensor. HOWEVER! After cycling up down 3 or so times with truck running it gets stuck in the up position again and will not come down. Same as when I'm usually driving around. It also won't raise any higher when confused like this and the compressor should still have another inch it could probably push it.. well I'm confused. Ideas?
 

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Discussion Starter #17 (Edited)
I'm down to maybe the height sensor or computer needing replacement. Maybe the potentiometer inside the switch starts sending the wrong voltage signal back to the computer? It's funny because I'll cycle it, get it to the right height manually by releasing all air that was built up. Shut off the truck and bolt it back to stock. Turn the truck on and 20sec later it jacks it up to 38", 2" too high. It's gone higher before too
 

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So.. Tested it all out. Everything works when truck running if I manually adjust the height sensor. HOWEVER! After cycling up down 3 or so times with truck running it gets stuck in the up position again and will not come down. Same as when I'm usually driving around. It also won't raise any higher when confused like this and the compressor should still have another inch it could probably push it.. well I'm confused. Ideas?
Is the compressor releasing the air when the sensor is activated to release? Or are you manually releasing the air?
 

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I'm down to maybe the height sensor or computer needing replacement. Maybe the potentiometer inside the switch starts sending the wrong voltage signal back to the computer? It's funny because I'll cycle it, get it to the right height manually by releasing all air that was built up. Shut off the truck and bolt it back to stock. Turn the truck on and 20sec later it jacks it up to 38", 2" too high. It's gone higher before too
It sounds as if the height sensor is not sending the signal on time or the computer not receiving the signal. I only had to mess with my compressor and strut, as I had them both leaking air. Do you know someone local that may lend you their height sensor for you to test? I would imagine that has to be cheaper than the computer or relay that received the message under the hood.
 

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Discussion Starter #20
So.. Tested it all out. Everything works when truck running if I manually adjust the height sensor. HOWEVER! After cycling up down 3 or so times with truck running it gets stuck in the up position again and will not come down. Same as when I'm usually driving around. It also won't raise any higher when confused like this and the compressor should still have another inch it could probably push it.. well I'm confused. Ideas?
Is the compressor releasing the air when the sensor is activated to release? Or are you manually releasing the air?
For the first 2 or 3 manual cycles it will release yes. I believe the relief value solenoid is working fine because of this. I've read in another thread that the computer can go into a fault mode and basically stop functioning or directing the compressor if it detects a bunch of bad conditions. I'm thinking this is what happens when I'm manually messing around with the height sensor. I never disconnected the lines anywhere. This was all just moving sensor arm up down
 
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