Jeep Air Suspension Woes

Brandon Technician Minnesota Posted   Latest  
Resolved
Chassis
Electrical
2014 Jeep Grand Cherokee Summit 3.6L (G ERB) 8-spd (845RE) — 1C4RJFJGXEC492433
C15a1-00 Unable To Obtain Desired Ride Height
C1562-98 Compressor Overtemp

I know these Jeeps have a bad track record for Quadra Lift air suspension issues, this one is a bit odd. These automatically drop about 0.6" at cruise speed into Aero Mode - this specific one consistently fails to lower the vehicle to Aero mode or Entry/Exit mode. I have my personal Grand Cherokee here to compare to, it's the exact same except mine is a V8.

Background info: 

  • New Mopar compressor and solenoid valve block assy (with new intake filter)
  • RR air spring is an Arnott brand (we did not replace)

When I lower the vehicle, sometimes the RR height sensor does not change values, sometimes it's the LF height sensor. This will typically trigger the air suspension fault message. During test drives, when it has been able to reach aero mode, it take forever to reach it. My Jeep is pretty instant once you reach the threshold speed, this one will take up to 30 seconds if it is successful. I understand this is a closed system with the ability to add air mass via outside air when necessary. Because I've never seen a vehicle have issues lowering, I'm stumped as to what the system thinks it is unable to do. The bags look to be in good condition, it's doesn't leak down overnight, lines have been checked with soapy water and are not leaking. I am able to deflate each individual spring via bidirectional controls. After compressor replacement, I did measure ride height and enter the new values into the ACSM. 

I've attached the screenshots for the measure air mass function, can see my wonky values. System air mass spec is 165-221 bar-L, which I'm within at 201 bar-L. You can see the LR air spring is at a much higher volume than the RR, at 29 bar-L. The LF spring seems low at 10 bar-L. The pressures are also not consistent from side to side either. You can also see that both front and rear left side springs are much lower than the other side, real world values are approx 3/4" lower on the left side than the right. It's strange that the LR is sitting low, but at a much higher pressure than any other springs. My height sensors are responsive watching live data on a road test, but I think my next course of action is to scope the ride height sensors at the ACSM and look for dropouts. 

diag​.​net/file/f2667vcj8…

diag​.​net/file/f742j1avn…

diag​.​net/file/f2i6d0669…

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Interesting
Daniel Owner
North Carolina
Daniel Default
 

I too, drive a 2018 Grand Cherokee. I thought the airbag system was just a nitrogen mover... Clearly I'm wrong.. Based on your data, I'd say there is probably moisture somewhere in the system, causing funky readings. If your ride height sensors are out of whack, then I could see the system trying to pump the pressure up to get them to raise, but realistically if you had that dramatic difference…

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Brandon Technician
Minnesota
Brandon Default
 

The SI is vague at best, but in theory it moves nitrogen back and forth, but if it needs to replenish airmass it will draw in 10L at a time through the filter/drier, then expel 5L out the intake to replenish the drier. It kind of makes the closed system/inert nitrogen idea moot in my opinion. I'm not sure how it measures airmass. It's a function in the scan tool, but as far as I'm aware there…

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Robert Mobile Technician
Michigan
Robert Default
 

Brandon is agree with Rick take a little closer look. Also, are you filling the system with Nitrogen or just shop air? Moisture can raise havoc in older systems.

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Brandon Technician
Minnesota
Brandon Default
 

I understand the concern with moisture. We don’t see enough of these to justify the nitrogen setup, unfortunately. For whatever it’s worth, we have a Kaiser Air Center with an integrated drier for painting, so the air that went in is pretty damn dry.

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Rick Technician
Illinois
Rick Default
 

I don't like the RR sensor values. It's reading higher than the left with lower pressure and less air mass. You rewrote the height sensor values? Why would you do that? I have never seen anyone able to do that successfully. Usually it is only necessary if the module is replaced and the best bet is to copy the values from the old module. If the old values are not available, it is usually best to…

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Allan Mechanic
Alberta
Allan Default
 

Why not just take the proper measurements and input those values? It’s not hard to do

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Brandon Technician
Minnesota
Brandon Default
   

A tech before me installed an eBay compressor and valve block, he mentioned something about relearning the height sensors. I didn't trust his work and wanted to make sure the correct measurements were programmed, plus I wasn’t sure how much the Arnott spring was a factor. I also refused to diag it until an OEM compressor and valve block were installed. I can sub in height values from my own WK2…

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Robert Mobile Technician
Michigan
Robert Default
 

Ok a few things have come out into the open. You mentioned an Ebay compressor was installed. Is this a used unit, aftermarket or New unit which was Mopar boxed? Secondly I know you said you utilized cleaned compressed air. But is this what the manufacturer calls for in the system? No, it calls for Nitrogen. You can make a set up similar to the OE tool for about 300 bucks and it works just fine…

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Brandon Technician
Minnesota
Brandon Default
 

It was diagnosed and a new eBay compressor and valve block, both separate parts from different vendors not a complete unit like OEM, were installed first by another tech. I installed a new, Mopar boxed compressor/valve block assembly from WorldPac. I understand the manufacturer wants nitro, I understand the reasoning behind using a stable inert gas in the system. I've already state my case to…

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Rick Technician
Illinois
Rick Default
   

When it does not lower properly, it gives the message "service air suspension", correct? No dtcs in the ascm? Are you able to run the height sensor check routine? No pinched or kinked lines? I don't know about the Arnott air bag, I have never used them so I can't say if that would have any affect. You also said it has trouble going to entry/exit, correct? If it was only while driving, there is…

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Brandon Technician
Minnesota
Brandon Default
 

It will attempt to lower at the correct speed, but once the 20 seconds are up for code set criteria, it will show a "Service Air Suspension Immediately" message on the EVIC and the Unable to Reach Desired Ride Height code is set as active. In the shop, if I put it into Sport mode, it will start lowering to Aero, but typically gives up after it lowers the front. I've gotten it to complete the…

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Rick Technician
Illinois
Rick Default
 

That is the star case. Those height readings look about right. Stupid question but No crossed lines? I have seen that done also. Probably by a color blind tech, but I have to ask. I am starting to think there is a restriction/kinked line. Basic operation of that system is the air (nitrogen) is just moved from the springs to the tank and vice versa. Compressor fills the springs or it fills the…

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Brandon Technician
Minnesota
Brandon Default
 

As far as I'm aware, no crossed lines. The only ones that were touched were at the compressor, spring circuit test actuates the correct spring. I agree with a pinched or kinked line though. I think I'm just having a hard time wrapping my head around easily going up and unable to go down, almost like it's functioning with check valves in the lines.

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Eric Owner/Technician
Wisconsin
Eric Default
 

That is exactly how a kinked or restricted line would act. Since you have high pressure available to raise the vehicle and only the low pressure in each spring to lower it a restriction would allow fast operation with the high pressure and slow operation with the low pressure. I'm not familiar with this system since I've never seen one. Can you lower one spring at a time using bi-directional…

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Rick Technician
Illinois
Rick Default
 

You can fill or vent springs one at a time. You can vent them to the reservoir or atmosphere. The system is not that complicated. It takes nitrogen from the reservoir and compresses it into the springs to raise. Lowering it takes the nitrogen from the springs and crams it back in the reservoir

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Brandon Technician
Minnesota
Brandon Default
 

That is a great analogy! Maybe I was assuming that the pressure behind the compressor would be the same going in both directions i.e. it would lift and lower at the same rate. I don't have a MicroPod/WiTech here, but on the Autel it allows bidirectional control to raise or lower all springs, or just raise/lower an individual circuit (spring).

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Rick Technician
Illinois
Rick Default
 

My line of thinking is that the compressor can push it to the springs. Can't pull it back. Could be a problem with the valve block too but I have never encountered that. If I was the unfortunate soul working on this, I would think about maybe switching lines front to rear and see if the problem follows.

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Brandon Technician
Minnesota
Brandon Update
   

Making some headway here. I ran each spring through the spring circuit test function. Rears both lower and raise quickly, I'm removing them from the equation for now. The LF bag deflates slowly. The RF bag doesn't deflate at all. I tried the deflate to reservoir and deflate to atmosphere functions, it doesn't move at all. I removed the line and released a small amount of air in the line, still…

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Rick Technician
Illinois
Rick Default
 

Forgive my ignorance but what are you referring to as a front pressure relief valve? Where did you disconnect the lines?

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Brandon Technician
Minnesota
Brandon Default
 

I disconnected the front springs right on top via the regular brass air fitting. The relief valve is the larger brass cylinder that threads directly into the top of the spring. Part number …AA. diag​.​net/file/f4f3xzn5d… ​

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Helpful
Interesting
Thanks
Rick Technician
Illinois
Rick Default
 

Thanks, I learned something. Never had to mess with one of those and I could find no mention of those in service info

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Eric Owner/Technician
Wisconsin
Eric Default
 

Glad you're making headway, it sure sounded like a restriction to me. High pressure could easily force the bags to fill but the lower pressure in the bags couldn't overcome the restriction. Similar to the same problem you see with a damaged rubber brake hose that allows you to apply the brake but won't allow the brake to release.

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Disagree
Michael Owner/Technician
Texas
Michael Default
 

I would make sure the height sensors are working correctly and in the correct position. I had a vehicle which I put the wrong sensor in (left/right) and one where the sensor links where damaged. Both where European Vehicles not a Jeep.

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Brandon Technician
Minnesota
Brandon Resolution
   

Replaced both front pressure relief valves today, refilled the system, performed air spring circuit tests on both front springs. They lower and raise quickly now. Road tested and vehicle will enter and exit Aero mode when expected. Entry/Exit mode also now works flawlessly. When I removed the LF air line today to replace the valve, it also wouldn't fully deflate the spring, that one must've been…

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Rick Technician
Illinois
Rick Default
 

Glad you got it fixed, I'm also glad you posted this. I learned something new. I have probably replaced over 100 compressors, dozens of springs a lot of lines but never those valves

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Anthony Technical Support Specialist
Pennsylvania
Anthony Default
 

Hi Rick: Due to the age of them, your track record very well may stay intact. Sometimes, you have to take the good with the bad. :) Guido

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Rick Technician
Illinois
Rick Default
 

Guido, you are 100% right. Personally I prefer my springs made out of metal, but what do I know?

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Anthony Technical Support Specialist
Pennsylvania
Anthony Default
 

Hi Rick: Living in the truck world for a few years, I've gotten to see the other side of the coin, up close. There are advantages to both. It should be needless to say, there are disadvantages to both also. The biggest difference between these two worlds is that trucks are spec'd, vocational vehicles if you will. (I understand that is a technical term and doesn't apply to all trucks but it…

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