How to diagnose HBMC problem?

[clinthammer]

I've noticed since late week that both rear sides of my 2016 QX80 are sagging slightly.


Today I knew I was correct because when I stood on either rear wheel to wash my roof, my feet barely fit in the wheel well (space between wheel and fender).


Today I was parked in my garage which has a slope so I moved the car to a flat road and heard the HBMC system auto levelling. The sagging was no more. I moved the car a couple of times and finally parked on a flat road without any sagging. About an hour later I drove past my car and saw it sagging.


The normal gap between wheel and fender is about 3.5 inches but when it sags it loses about an inch.


Anyone else face issues with their HBMC system like this? Would the Infiniti tech (not dealer) would be able to pull any codes from the car?

 

[marctronixx]

what you heard was the auto leveling pump for the air in the shocks. the hbmc is a system of hydraulic fluid with sensors and piping that adapts to changes in driving.

 

[clinthammer]

what you heard was the auto leveling pump for the air in the shocks. the hbmc is a system of hydraulic fluid with sensors and piping that adapts to changes in driving.

Thank you for the clarification. So it's likely an issue with the shocks leaking since the pump is working?

 

[clinthammer]

Issue

• Sagging is equal on both sides
• Sags gradually when turned off and at rest
• Inflates and lifts ~1.5 inches upon starting and driving

Today I noticed the rear sagging on both sides. Turned on the car moved it back and forth and heard the rear compressor ON. After about 2-3 minutes the rear optimal ride height was reached. I could fit a plastic bottle between the well nicely.

Once the compressor was OFF, after 2 minutes I noticed the sagging and it finished sagging 4 minutes later. Could barely fit the same plastic bottle.

Could it be the compressor or sensor?

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[marctronixx]

sounds like compressor and level sensor are working fine. you may have a leaky hose or shock since you say it starts to sag when the car is off. one way to test in the future, is , with the car off, open the hatch and sit 2 or 3 human people on the end ( or comparable weight), then turn on the car. if the sensor is working, it will trigger the pump/compressor, so you dont have to move the car to activate it.

 

[clinthammer]

I have a feeling it's a leak hose because both shocks are facing the same issue at same time. Even today morning when I started the car, the pump turned on and raised the car. Once I got to work 25 mins later, I saw it sagging by 0.75-1inch.

Will be taking car to my garage on Friday to check for leaks.

Thanks for all the advice.

 

[primov8]

From what you’re describing, I doubt it’s the air lines because if they were leaking, the rear air leveling shocks wouldn’t be able to reach operating height. But it’s easy to check for leaks. Just mix a soap + water solution where all the air lines connect to; shocks and air leveling compressor. At least those get ruled out.

The problem is likely the air leveling compressor itself. The exhaust valve solenoid built-in the compressor is notorious for failing on these things. When it starts to fail, the compressor will inflate the air shocks but the exhaust valve solenoid gets stuck and air releases from the system when it’s not supposed to do so.

 

[clinthammer]

Had the vehicle lifted and checked today. The rear driver shock absorber had an ugly leak. They didn't not find any other leaks.

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[marctronixx]

so just one shock and not the other? did you end up replacing both or just one or what did you end up doing? glad to hear its not something more serious.

 

[clinthammer]

Yeah it was just the one shock but I am going to end up replacing both rear shocks since they are both 7 years old. Will get it done next week once parts are in.

 

[marctronixx]

cool glad it worked out...

 

[hubolei]

I have 19 QX80 with HBMC. One HBMC high pressure line failed and one shock at the rear was leaking air. These air/Hydraulic shocks designed for 100k miles. You can replace the shocks, but to bleed the HBMC system you need a special hand pump from Nissan which will cost $3000+. The Nissan dealer quoted me $3500(Canadian$) for two rear shocks and bleeding. I decided to do it myself. I bought a similar high pressure pump (HBMC requires 330psi in the system) from overseas, two shocks from Nissan dealer here in Toronto ($1700), and hydraulic suspension fluid from Toyota (they use the same, even its different part#, you can cross reference with Revanol AHC fluid from Germany).After replacing shocks and coil spring, my 12yo son and I just finished the first bleeding procedure on 4 corners yesterday. The car drives ok, not as bouncy as before, but still soft. We will do another round this morning, hopefully it fix the problem. The HBMC gives comfort when they work, but when they fail, no mechanic shop other than Nissan or Infiniti can even fix it. I hope this gives QX80 owners some ideas where to begin when the suspension system starts failing.

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