Rear air suspension sagging

Sid3ways

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I’m running into a slightly similar issue on my 2012 QX56 with the air/hydraulic shocks. After a tire change at the shop, I’ve noticed the rear end of the suv is now squatting. Started to do some searching online and it seems a lot of issues are from the lines and fittings but don’t speak about the hydraulic shocks, do those suffer the same issue?

Anyways, initially I don’t hear the pump coming on when I start the vehicle. So we hooked 12V up directly to the pump and the pump fires up. Seeing as though the pump functions we then took the level sensor arm off, and pushed it up (with ignition on and also engine running) and never had the pump kick on. The vehicle was still on the hoist so the front tires weren’t on the ground (don’t know if it knows somethings up if front has no load and the rear shows a load so it doesn’t trigger the pump?).
At that point we just manually triggered the pump to run by hooking up directly (without vehicle harness connected) and it eventually pumped the rear up to regular ride height and we heard it click and it shut off on its own (is there a pressure switch?). I drove it home from my friends shop which is about 5 miles away and it had settled back down by the time I got home so I assume there’s a leak too. Is it possible the system thinks it’s constantly too high so it tells it to bleed off air when it shouldn’t?
I see there are a few relays according to a manual I saw but I could only find one relay to test and the relay was fine. I couldn’t find the fuse, which fuse is it?

Thank You for any help you can provide!
 

primov8

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Any chance your truck was turned to ignition or started while on the lift? If so, you'll need a full range scan tool (none of those pocket scanners) to diagnose any DTCs related to the auto leveling suspension and to reset and initialize ride height it if there are no DTCs or leaks found.
 
G

G-3980

Ok that could be the case, I don’t recall if it was started on the lift or not. Does Amazon sell anything that does it all?
 

primov8

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I'm sure Amazon does but can't say which brand or model specifically as there are so many options out there. Does your friend's shop have a scan tool? If so, the shop can check if it'll read the BCM. If it does, then the auto leveling module/system can be diagnosed as well. I know on my Autel MP808TS, the auto leveling system is categorized as E-SUS so it may be different on other scan tools.
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Sid3ways

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He unfortunately doesn't have a powerful enough scanner to do those functions and I certainly don't want to spend 1K for a one-time use scenario here (I'm trying to bring the vehicle up to part to list it for sale). I wish I could find someone who had one of these units so I could plug it in and see if it worked :(
 

primov8

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Without having to spend more than what’s needed, find a local shop that has a full range diagnostic tool. It shouldn’t take no more than a couple minutes to read, reset and set back to OE height.
 

Sid3ways

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Good call, I am stopping by a shop that has a higher end unit to hopefully see how I can reset the system. Any trips or instructions on how to do the whole process on your unit (his is an Autel as well I believe).
 

primov8

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As long as their diagnostic tool can read the BCM, then you’re good. The tech can choose E-SUS and scan for any DTCs and even observe live data. From there on, it’s pretty much self intuitive because the Autel will display the different prompts under E-SUS.
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gpschmidt

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You wouldn't happen to have a picture of what you mean by "sagging", would you? I would say my 56 has a little sag in the rear, but I'm judging by the gap between the wheel wells on the front vs. the back. The car frame appears to be sitting level, however...
 

Sid3ways

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Do you know the exact process? I was able to clear the codes and they stayed off. We then clicked the reset ride height but it was sagging at that time. I thought that it would pump up and level itself but it didn’t. I went ahead and had it manually turn on the pump to see if it would stay but I drove away and now thinking I messed something up (I’m doing this on my own with their tool) and reset the ride height as the new sagging level. It’s back to sagging in 5 minutes. Is that a leak or did it let the air out because it thinks the sagging level is now the “norm”.
There were three options on the special functions page, can you provide the exact process of what to do? It wasn’t cut and dry for me on the Autel.
Thanks!!!
 

Sid3ways

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What codes did your truck have?
I didn’t take a picture unfortunately. There was one current code showing and 2 old ones. I think it just said ride leveling or something though I can’t say for certain. They all cleared out. I’m going back tomorrow and I hope I can pull the codes again and try to do this right this time. I recall going to the middle option and I clicked ok and then it failed. Then the third option allowed me to delete the current level setting maybe? So I went back to the 2nd option and it said it did whatever that was. I’ll be honest I’m going off of a bad memory though.

I was hoping it was easier to understand but I wasn’t sure what order things had to be done. When it relearns do you have to tell it pump up to the level you need before you tell it to set new height? I was hoping it would do it all on its own but I guess not. Should the compressor run on any of those settings, because it didn’t unless we triggered it?
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primov8

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Yes, the compressor is supposed to run when prompted when choosing either "adjust height ini" and "standard level/height."
Since you mentioned the bags deflated after 5 mins and if the DTC is a C1803, then the exhaust valve solenoid built inside the compressor is likely stuck open. It happened to my '14 QX80 last year and I ended up replacing it with a new compressor.
 

Sid3ways

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Yes, the compressor is supposed to run when prompted when choosing either "adjust height ini" and "standard level/height."
Since you mentioned the bags deflated after 5 mins and if the DTC is a C1803, then the exhaust valve solenoid built inside the compressor is likely stuck open. It happened to my '14 QX80 last year and I ended up replacing it with a new compressor.
I’ll check tomorrow. We could cycle the exhaust valve and it seemed to hold or go down quick when we activated it. I’ll double check though and make sure what I remember is correct. May we do need a new compressor. I hope it’s that easy. I’ll see what the code is if there is still one showing.
 

Jccorb

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I would go with the compressor. My 15 was doing the same thing replaced the rear shocks not cheap of course. While I was under there I replaced the the front struts and springs. Over night it would deflate again. Bought a doorman compressor from Amazon that I had to modify to fit to the OE mount, and the level switch. After install holds over night and no issues.
You may wonder why I did all the extra work it is because I bought it used with 115k on it and it was 5 years old. Peace of mind. Also replaced both rear CATS and now onto the fronts. All Nissan parts because can’t trust aftermarket cats and OE is stainless.
 

Sid3ways

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So I took it back to the shop and the 2nd time, realized I probably F'd up the default ride height considering it says you have to calibrate it with the wheels off the ground, I definitely did NOT do that.

All of his lifts were being used unfortunately, anyways, I ordered myself the same Autel MaxiPro unit so I can do it at my friends shop. Here are the pictures I took of the faults by the way. It did complain about the height sensor so I'm going to change that out assuming the proper retrain procedure doesn't work this weekend. I do think my compressor and shocks are good as we manually pumped them up and it held ride height for 20 minutes with no sag. When I put the vehicle into drive it almost immediately opened the valve and down it went (which it must think sagging is the now "proper" right height due to me screwing up the init process). The height sensor was showing 4.9-4.94 volts, is that in normal range?






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primov8

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Don't change out the height level sensor just yet as that may have been triggered because of the C1805. Also, you don't need all four wheels lifted off the ground as the air leveling system is only really applicable to the rear suspension.

With the engine running, jack up the rear end and make sure the rear wheels are completely off the ground. Now that you have the diagnostic tool, go to E-SUS and active tests. Turn on the compressor for about 1 min. and the CK SUSP light should come on. If not, perform this procedure again until the light comes on.

Once the light is on, go to Adjust height ini and start. The CK SUSP light should turn off once this is completed. Now drop the rear end, wheels on the ground and select Standard height level. Give it about 2-3 mins and go to live data and look for VHCL HGT CNVSN VL. The acceptable range should be between -15 to 15mm.
 

Sid3ways

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That is great info primov, I do have a question though. You said turn on the compressor for 1 minute while the rear wheels are in the air and the ck susp like should come on, when you say perform the procedure again, do you mean to let all of the air out and then pump it up again for a minute?

Once again, thanks for all of the help here, you surely saved me a bunch of money :)
 

primov8

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That is great info primov, I do have a question though. You said turn on the compressor for 1 minute while the rear wheels are in the air and the ck susp like should come on, when you say perform the procedure again, do you mean to let all of the air out and then pump it up again for a minute?

Once again, thanks for all of the help here, you surely saved me a bunch of money :)
Only perform the procedure again if the CK SUSP light doesn’t come on. The light has to be on to go onto the next step.
 

Sid3ways

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I want to pop back in here to provide an update for people to search for in the future. Well, I received the Autel unit but the same day, the vehicle fixed itself and went back up to normal ride height. I figured I'd give it a few days to see if it would stay and it did for about a week and a half. Just last night now I noticed that the car is back down to the sagging position. I think it's clear the suspension itself holds air perfectly fine since it worked great for a week (and the car sat off for hours and hours and never sagged). It has to be the sensor itself (which is the error I was getting), it's probably periodically now going out of range?

So I'm going to look for a height module, any recommendations on the best place to order one of those? I see a ton of them online for up to the year 2010 or 2011, nothing for 2012 on up.

I wanted to ping this thread again as I'm having trouble finding a ride height sensor for the 2012. It seems like everything online says it works up to 2010, there is no mention these will work for 2012 even though the pictures look similar. Any thoughts?
 
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